diff --git a/bundles/org.openhab.core.automation/src/main/java/org/openhab/core/automation/type/Input.java b/bundles/org.openhab.core.automation/src/main/java/org/openhab/core/automation/type/Input.java
index 273f9343460..66856788342 100644
--- a/bundles/org.openhab.core.automation/src/main/java/org/openhab/core/automation/type/Input.java
+++ b/bundles/org.openhab.core.automation/src/main/java/org/openhab/core/automation/type/Input.java
@@ -14,6 +14,8 @@
 
 import java.util.Set;
 
+import org.eclipse.jdt.annotation.NonNullByDefault;
+import org.eclipse.jdt.annotation.Nullable;
 import org.openhab.core.automation.Module;
 import org.openhab.core.automation.Rule;
 
@@ -32,20 +34,26 @@
  * "temperature", for example. The value "*" means that all possible types are acceptable. The type is used to determine
  * which {@link Output} can be connected to this {@link Input}.</li>
  * <li>label (optional) - short description (one word) of the {@link Input}</li>
- * <li>description (optional) - long user friendly description of the {@link Input}</li>
+ * <li>description (optional) - long user-friendly description of the {@link Input}</li>
+ * <li>tags (optional) - add additional restrictions to connections between {@code Input}s and {@link Output}s. The
+ * input tags must be subset of the output tags to succeed the connection.</li>
+ * <li>required (optional) - defines if the {@link Input} is required or optional. The default value is false.</li>
+ * <li>reference (optional) - refers to the input of parent module type or null. If this input is part of the system
+ * module the reference should be null.</li>
  * <li>default value (optional) - the string representation of the default value of the {@link Input}. It must be
  * compatible with the type of the {@link Input}</li>
- * <li>required (optional) - defines if the {@link Input} is required or optional. The default value is false.</li>
  * </ul>
  *
  * @author Yordan Mihaylov - Initial contribution
+ * @author Florian Hotze - Add null annotations
  */
+@NonNullByDefault
 public class Input {
 
     /**
      * Specifies a unique name of the {@code Input} in scope of the {@link Module}.
      */
-    private String name;
+    private @NonNullByDefault({}) String name;
 
     /**
      * Specifies the acceptable data type for this {@link Input}. The value could be any string that makes sense for the
@@ -53,25 +61,25 @@ public class Input {
      * value "*" means that all possible types are acceptable. The type is used to determine which {@link Output} can be
      * connected to this {@link Input} instance.
      */
-    private String type;
+    private @NonNullByDefault({}) String type;
 
     /**
      * Keeps a single word description of the {@code Input}.
      */
-    private String label;
+    private @Nullable String label;
 
     /**
-     * Keeps the user friendly description of the {@code Input}.
+     * Keeps the user-friendly description of the {@code Input}.
      */
-    private String description;
+    private @Nullable String description;
 
     /**
      * Determines if the {@code Input} is required or optional.
      */
     private boolean required = false;
-    private Set<String> tags;
-    private String reference;
-    private String defaultValue;
+    private @Nullable Set<String> tags;
+    private @Nullable String reference;
+    private @Nullable String defaultValue;
 
     /**
      * Default constructor for deserialization e.g. by Gson.
@@ -98,12 +106,12 @@ public Input(String name, String type) {
      * @param name unique name of the {@code Input} in scope of the module.
      * @param type the acceptable data type for this {@link Input}.
      * @param label a single word description of the {@code Input}.
-     * @param description user friendly description of the {@code Input}.
-     * @param tags are associated with the {@code Input}. The tags adds additional restrictions to connections
+     * @param description user-friendly description of the {@code Input}.
+     * @param tags are associated with the {@code Input}. The tags add additional restrictions to connections
      *            between {@code Input}s and {@link Output}s. The input tags must be subset of the output tags
      *            to succeed the connection.
      *            For example: When we want to connect input to output and both have same java.lang.double data
-     *            type. The the output has assign "temperature" and "celsius" tags then the input must have at
+     *            type. The output has assign "temperature" and "celsius" tags then the input must have at
      *            least one of these output's tags (i.e. "temperature") to connect this {@code Input} to the
      *            selected output.
      * @param required determines if the {@code Input} is required or optional.
@@ -113,8 +121,8 @@ public Input(String name, String type) {
      *            must be the type the Input.
      * @throws IllegalArgumentException If one of the name or type parameters is null.
      */
-    public Input(String name, String type, String label, String description, Set<String> tags, boolean required,
-            String reference, String defaultValue) {
+    public Input(String name, String type, @Nullable String label, @Nullable String description,
+            @Nullable Set<String> tags, boolean required, @Nullable String reference, @Nullable String defaultValue) {
         if (name == null) {
             throw new IllegalArgumentException("The name of the input must not be NULL!");
         }
@@ -145,16 +153,16 @@ public String getName() {
      *
      * @return label of the Input.
      */
-    public String getLabel() {
+    public @Nullable String getLabel() {
         return label;
     }
 
     /**
      * Gets the long description of the Input.
      *
-     * @return user friendly description of the Input.
+     * @return user-friendly description of the Input.
      */
-    public String getDescription() {
+    public @Nullable String getDescription() {
         return description;
     }
 
@@ -188,6 +196,7 @@ public String getType() {
      * @return tags associated with this Input.
      */
     public Set<String> getTags() {
+        Set<String> tags = this.tags;
         return tags != null ? tags : Set.of();
     }
 
@@ -197,7 +206,7 @@ public Set<String> getTags() {
      *
      * @return reference to data source.
      */
-    public String getReference() {
+    public @Nullable String getReference() {
         return reference;
     }
 
@@ -207,7 +216,7 @@ public String getReference() {
      *
      * @return the string representation of the default value of this {@link Input}.
      */
-    public String getDefaultValue() {
+    public @Nullable String getDefaultValue() {
         return defaultValue;
     }
 
diff --git a/bundles/org.openhab.core.config.core/src/main/java/org/openhab/core/config/core/ConfigDescriptionParameter.java b/bundles/org.openhab.core.config.core/src/main/java/org/openhab/core/config/core/ConfigDescriptionParameter.java
index aea9ca011d7..8676ad369e0 100644
--- a/bundles/org.openhab.core.config.core/src/main/java/org/openhab/core/config/core/ConfigDescriptionParameter.java
+++ b/bundles/org.openhab.core.config.core/src/main/java/org/openhab/core/config/core/ConfigDescriptionParameter.java
@@ -18,6 +18,9 @@
 import java.util.List;
 import java.util.Set;
 
+import org.eclipse.jdt.annotation.NonNullByDefault;
+import org.eclipse.jdt.annotation.Nullable;
+
 import com.google.gson.annotations.SerializedName;
 
 /**
@@ -38,7 +41,9 @@
  *         getter to return primitive types
  * @author Thomas Höfer - Added unit
  * @author Laurent Garnier - Removed constraint on unit value
+ * @author Florian Hotze - Add null annotations
  */
+@NonNullByDefault
 public class ConfigDescriptionParameter {
 
     /**
@@ -73,27 +78,27 @@ public enum Type {
 
     }
 
-    private String name;
-    private Type type;
+    private @NonNullByDefault({}) String name;
+    private @NonNullByDefault({}) Type type;
 
-    private String groupName;
+    private @Nullable String groupName;
 
-    private BigDecimal min;
-    private BigDecimal max;
-    private BigDecimal step;
-    private String pattern;
+    private @Nullable BigDecimal min;
+    private @Nullable BigDecimal max;
+    private @Nullable BigDecimal step;
+    private @Nullable String pattern;
     private boolean required = false;
     private boolean readOnly = false;
     private boolean multiple = false;
-    private Integer multipleLimit;
-    private String unit;
-    private String unitLabel;
+    private @Nullable Integer multipleLimit;
+    private @Nullable String unit;
+    private @Nullable String unitLabel;
 
-    private String context;
+    private @Nullable String context;
     @SerializedName("default")
-    private String defaultValue;
-    private String label;
-    private String description;
+    private @Nullable String defaultValue;
+    private @Nullable String label;
+    private @Nullable String description;
 
     private List<ParameterOption> options = new ArrayList<>();
     private List<FilterCriteria> filterCriteria = new ArrayList<>();
@@ -116,29 +121,23 @@ public ConfigDescriptionParameter() {
     /**
      * Creates a new instance of this class with the specified parameters.
      *
-     * @param name the name of the configuration parameter (must neither be null
-     *            nor empty)
-     * @param type the data type of the configuration parameter (nullable)
+     * @param name the name of the configuration parameter (must not be empty)
+     * @param type the data type of the configuration parameter
      * @param minimum the minimal value for numeric types, or the minimal length of
-     *            strings, or the minimal number of selected options (nullable)
+     *            strings, or the minimal number of selected options
      * @param maximum the maximal value for numeric types, or the maximal length of
-     *            strings, or the maximal number of selected options (nullable)
-     * @param stepsize the value granularity for a numeric value (nullable)
-     * @param pattern the regular expression for a text type (nullable)
+     *            strings, or the maximal number of selected options
+     * @param stepsize the value granularity for a numeric value
+     * @param pattern the regular expression for a text type
      * @param required specifies whether the value is required
      * @param readOnly specifies whether the value is read-only
      * @param multiple specifies whether multiple selections of options are allowed
-     * @param context the context of the configuration parameter (can be null or
-     *            empty)
-     * @param defaultValue the default value of the configuration parameter (can be null)
-     * @param label a human readable label for the configuration parameter (can be
-     *            null or empty)
-     * @param description a human readable description for the configuration parameter
-     *            (can be null or empty)
-     * @param filterCriteria a list of filter criteria for values of a dynamic selection
-     *            list (nullable)
+     * @param context the context of the configuration parameter (can be empty)
+     * @param defaultValue the default value of the configuration parameter
+     * @param label a human-readable label for the configuration parameter (can be empty)
+     * @param description a human-readable description for the configuration parameter (can be empty)
+     * @param filterCriteria a list of filter criteria for values of a dynamic selection list
      * @param options a list of element definitions of a static selection list
-     *            (nullable)
      * @param groupName a string used to group parameters together into logical blocks
      *            so that the UI can display them together
      * @param advanced specifies if this is an advanced parameter. An advanced
@@ -151,10 +150,11 @@ public ConfigDescriptionParameter() {
      *            can enter values other than those in the list
      * @param multipleLimit specifies the maximum number of options that can be selected
      *            when multiple is true
-     * @param unit specifies the unit of measurements for the configuration parameter (nullable)
+     * @param unit specifies the unit of measurements for the configuration parameter
      * @param unitLabel specifies the unit label for the configuration parameter. This attribute can also be used to
      *            provide
      *            natural language units as iterations, runs, etc.
+     * @param verify specifies whether the parameter should be considered dangerous
      * @throws IllegalArgumentException
      *             <ul>
      *             <li>if the name is null or empty, or the type is null</li>
@@ -166,11 +166,14 @@ public ConfigDescriptionParameter() {
      * @deprecated Use {@link ConfigDescriptionParameterBuilder} instead.
      */
     @Deprecated
-    ConfigDescriptionParameter(String name, Type type, BigDecimal minimum, BigDecimal maximum, BigDecimal stepsize,
-            String pattern, Boolean required, Boolean readOnly, Boolean multiple, String context, String defaultValue,
-            String label, String description, List<ParameterOption> options, List<FilterCriteria> filterCriteria,
-            String groupName, Boolean advanced, Boolean limitToOptions, Integer multipleLimit, String unit,
-            String unitLabel, Boolean verify) throws IllegalArgumentException {
+    ConfigDescriptionParameter(String name, Type type, @Nullable BigDecimal minimum, @Nullable BigDecimal maximum,
+            @Nullable BigDecimal stepsize, @Nullable String pattern, @Nullable Boolean required,
+            @Nullable Boolean readOnly, @Nullable Boolean multiple, @Nullable String context,
+            @Nullable String defaultValue, @Nullable String label, @Nullable String description,
+            @Nullable List<ParameterOption> options, @Nullable List<FilterCriteria> filterCriteria,
+            @Nullable String groupName, @Nullable Boolean advanced, @Nullable Boolean limitToOptions,
+            @Nullable Integer multipleLimit, @Nullable String unit, @Nullable String unitLabel,
+            @Nullable Boolean verify) throws IllegalArgumentException {
         if ((name == null) || (name.isEmpty())) {
             throw new IllegalArgumentException("The name must neither be null nor empty!");
         }
@@ -233,7 +236,7 @@ public ConfigDescriptionParameter() {
     /**
      * Returns the name of the configuration parameter.
      *
-     * @return the name of the configuration parameter (neither null, nor empty)
+     * @return the name of the configuration parameter (not empty)
      */
     public String getName() {
         return this.name;
@@ -242,7 +245,7 @@ public String getName() {
     /**
      * Returns the data type of the configuration parameter.
      *
-     * @return the data type of the configuration parameter (not null)
+     * @return the data type of the configuration parameter
      */
     public Type getType() {
         return this.type;
@@ -250,17 +253,17 @@ public Type getType() {
 
     /**
      * @return the minimal value for numeric types, or the minimal length of
-     *         strings, or the minimal number of selected options (nullable)
+     *         strings, or the minimal number of selected options
      */
-    public BigDecimal getMinimum() {
+    public @Nullable BigDecimal getMinimum() {
         return min;
     }
 
     /**
      * @return the maximal value for numeric types, or the maximal length of
-     *         strings, or the maximal number of selected options (nullable)
+     *         strings, or the maximal number of selected options
      */
-    public BigDecimal getMaximum() {
+    public @Nullable BigDecimal getMaximum() {
         return max;
     }
 
@@ -269,23 +272,23 @@ public BigDecimal getMaximum() {
      * <p>
      * By setting the step size to <code>0</code>, any granularity is allowed, i.e. any number of decimals is accepted.
      *
-     * @return the value granularity for a numeric value (nullable)
+     * @return the value granularity for a numeric value
      */
-    public BigDecimal getStepSize() {
+    public @Nullable BigDecimal getStepSize() {
         return step;
     }
 
     /**
-     * @return the regular expression for a text type (nullable)
+     * @return the regular expression for a text type
      */
-    public String getPattern() {
+    public @Nullable String getPattern() {
         return pattern;
     }
 
     /**
      * @return true if the value is required, otherwise false.
      */
-    public Boolean isReadOnly() {
+    public boolean isReadOnly() {
         return readOnly;
     }
 
@@ -293,14 +296,14 @@ public Boolean isReadOnly() {
      * @return true if multiple selections of options are allowed, otherwise
      *         false.
      */
-    public Boolean isMultiple() {
+    public boolean isMultiple() {
         return multiple;
     }
 
     /**
      * @return the maximum number of options that can be selected from the options list
      */
-    public Integer getMultipleLimit() {
+    public @Nullable Integer getMultipleLimit() {
         return multipleLimit;
     }
 
@@ -347,10 +350,9 @@ public Integer getMultipleLimit() {
      * - location: A latitude,longitude[,altitude] GPS location. A user-interface would probably render a world map for
      * selection.
      *
-     * @return the context of the configuration parameter (could be null or
-     *         empty)
+     * @return the context of the configuration parameter (could be empty)
      */
-    public String getContext() {
+    public @Nullable String getContext() {
         return this.context;
     }
 
@@ -362,35 +364,34 @@ public String getContext() {
      *         false
      */
     public boolean isRequired() {
-        return this.required;
+        return required;
     }
 
     /**
      * Returns the default value of the configuration parameter.
      *
-     * @return the default value of the configuration parameter (could be null)
+     * @return the default value of the configuration parameter
      */
-    public String getDefault() {
-        return this.defaultValue;
+    public @Nullable String getDefault() {
+        return defaultValue;
     }
 
     /**
-     * Returns a human readable label for the configuration parameter.
+     * Returns a human-readable label for the configuration parameter.
      *
-     * @return a human readable label for the configuration parameter (could be
-     *         null or empty)
+     * @return a human-readable label for the configuration parameter (could be empty)
      */
-    public String getLabel() {
-        return this.label;
+    public @Nullable String getLabel() {
+        return label;
     }
 
     /**
-     * Returns a the group for this configuration parameter.
+     * Returns the group for this configuration parameter.
      *
-     * @return a group for the configuration parameter (could be null or empty)
+     * @return a group for the configuration parameter (could be empty)
      */
-    public String getGroupName() {
-        return this.groupName;
+    public @Nullable String getGroupName() {
+        return groupName;
     }
 
     /**
@@ -400,7 +401,7 @@ public String getGroupName() {
      * @return true if the value is limited to the options list
      */
     public boolean getLimitToOptions() {
-        return this.limitToOptions;
+        return limitToOptions;
     }
 
     /**
@@ -409,17 +410,16 @@ public boolean getLimitToOptions() {
      * @return true if the value is an advanced option
      */
     public boolean isAdvanced() {
-        return this.advanced;
+        return advanced;
     }
 
     /**
-     * Returns a human readable description for the configuration parameter.
+     * Returns a human-readable description for the configuration parameter.
      *
-     * @return a human readable description for the configuration parameter
-     *         (could be null or empty)
+     * @return a human-readable description for the configuration parameter (could be empty)
      */
-    public String getDescription() {
-        return this.description;
+    public @Nullable String getDescription() {
+        return description;
     }
 
     /**
@@ -428,7 +428,7 @@ public String getDescription() {
      * @return static selection list for the value of this parameter
      */
     public List<ParameterOption> getOptions() {
-        return this.options;
+        return options;
     }
 
     /**
@@ -440,24 +440,24 @@ public List<ParameterOption> getOptions() {
      * @return list of filter criteria for a dynamically created selection list
      */
     public List<FilterCriteria> getFilterCriteria() {
-        return this.filterCriteria;
+        return filterCriteria;
     }
 
     /**
      * Returns the unit of measurements of this parameter.
      *
-     * @return the unit of measurements of this parameter (could be null)
+     * @return the unit of measurements of this parameter
      */
-    public String getUnit() {
+    public @Nullable String getUnit() {
         return unit;
     }
 
     /**
      * Returns the unit label of this parameter.
      *
-     * @return the unit label of this parameter (could be null)
+     * @return the unit label of this parameter
      */
-    public String getUnitLabel() {
+    public @Nullable String getUnitLabel() {
         return unitLabel;
     }
 
@@ -467,7 +467,7 @@ public String getUnitLabel() {
      *
      * @return true if the parameter requires verification in the UI
      */
-    public Boolean isVerifyable() {
+    public boolean isVerifyable() {
         return verify;
     }
 
diff --git a/bundles/org.openhab.core.config.core/src/main/java/org/openhab/core/config/core/ConfigUtil.java b/bundles/org.openhab.core.config.core/src/main/java/org/openhab/core/config/core/ConfigUtil.java
index d99c8314938..294b8617ada 100644
--- a/bundles/org.openhab.core.config.core/src/main/java/org/openhab/core/config/core/ConfigUtil.java
+++ b/bundles/org.openhab.core.config.core/src/main/java/org/openhab/core/config/core/ConfigUtil.java
@@ -68,7 +68,10 @@ public class ConfigUtil {
     }
 
     static @Nullable Object getDefaultValueAsCorrectType(String parameterName, Type parameterType,
-            String defaultValue) {
+            @Nullable String defaultValue) {
+        if (defaultValue == null) {
+            return null;
+        }
         try {
             switch (parameterType) {
                 case TEXT:
diff --git a/bundles/org.openhab.core.config.core/src/main/java/org/openhab/core/config/core/internal/validation/PatternValidator.java b/bundles/org.openhab.core.config.core/src/main/java/org/openhab/core/config/core/internal/validation/PatternValidator.java
index a0b288661ec..c52c8537f25 100644
--- a/bundles/org.openhab.core.config.core/src/main/java/org/openhab/core/config/core/internal/validation/PatternValidator.java
+++ b/bundles/org.openhab.core.config.core/src/main/java/org/openhab/core/config/core/internal/validation/PatternValidator.java
@@ -29,11 +29,12 @@ final class PatternValidator implements ConfigDescriptionParameterValidator {
 
     @Override
     public @Nullable ConfigValidationMessage validate(ConfigDescriptionParameter parameter, @Nullable Object value) {
-        if (value == null || parameter.getType() != Type.TEXT || parameter.getPattern() == null) {
+        String pattern = parameter.getPattern();
+        if (value == null || parameter.getType() != Type.TEXT || pattern == null) {
             return null;
         }
 
-        if (!((String) value).matches(parameter.getPattern())) {
+        if (!((String) value).matches(pattern)) {
             MessageKey messageKey = MessageKey.PATTERN_VIOLATED;
             return new ConfigValidationMessage(parameter.getName(), messageKey.defaultMessage, messageKey.key,
                     String.valueOf(value), parameter.getPattern());
diff --git a/bundles/org.openhab.core.io.rest.core/src/main/java/org/openhab/core/io/rest/core/config/EnrichedConfigDescriptionParameterDTO.java b/bundles/org.openhab.core.io.rest.core/src/main/java/org/openhab/core/io/rest/core/config/EnrichedConfigDescriptionParameterDTO.java
index 88afee855e6..8a3ac461ea1 100644
--- a/bundles/org.openhab.core.io.rest.core/src/main/java/org/openhab/core/io/rest/core/config/EnrichedConfigDescriptionParameterDTO.java
+++ b/bundles/org.openhab.core.io.rest.core/src/main/java/org/openhab/core/io/rest/core/config/EnrichedConfigDescriptionParameterDTO.java
@@ -18,8 +18,6 @@
 import java.util.Set;
 import java.util.stream.Stream;
 
-import org.eclipse.jdt.annotation.NonNullByDefault;
-import org.eclipse.jdt.annotation.Nullable;
 import org.openhab.core.config.core.ConfigDescriptionParameter.Type;
 import org.openhab.core.config.core.dto.ConfigDescriptionParameterDTO;
 import org.openhab.core.config.core.dto.FilterCriteriaDTO;
@@ -31,16 +29,15 @@
  *
  * @author Christoph Weitkamp - Initial contribution
  */
-@NonNullByDefault
 public class EnrichedConfigDescriptionParameterDTO extends ConfigDescriptionParameterDTO {
 
     private static final String DEFAULT_LIST_DELIMITER = ",";
 
-    public @Nullable Collection<String> defaultValues;
+    public Collection<String> defaultValues;
 
     public EnrichedConfigDescriptionParameterDTO(String name, Type type, BigDecimal minimum, BigDecimal maximum,
             BigDecimal stepsize, String pattern, Boolean required, Boolean readOnly, Boolean multiple, String context,
-            @Nullable String defaultValue, String label, String description, List<ParameterOptionDTO> options,
+            String defaultValue, String label, String description, List<ParameterOptionDTO> options,
             List<FilterCriteriaDTO> filterCriteria, String groupName, Boolean advanced, Boolean limitToOptions,
             Integer multipleLimit, String unit, String unitLabel, Boolean verify) {
         super(name, type, minimum, maximum, stepsize, pattern, required, readOnly, multiple, context, defaultValue,