Don't serialized empty delimited lists

src/main/java/com/github/trickl/jackson/module/httpquery/ser/HttpQuerySerializer.java

@@ -1,5 +1,6 @@
 package com.github.trickl.jackson.module.httpquery.ser;
 
+import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.core.JsonFactory;
 import com.fasterxml.jackson.core.JsonGenerator;
 import com.fasterxml.jackson.databind.BeanDescription;
@@ -130,7 +131,7 @@ public void writeNameValue(
           }
 
           HttpQueryDelimited annotatedList = prop.findAnnotation(HttpQueryDelimited.class);
-          if (annotatedList != null) {
+          if (annotatedList != null && !collection.isEmpty()) {             
             HttpQueryDelimitedSerializer serializer =
                 new HttpQueryDelimitedSerializer(
                     propType,

src/test/java/com/github/trickl/jackson/module/httpquery/EmptyListsTest.java

@@ -0,0 +1,134 @@
+package com.github.trickl.jackson.module.httpquery;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.github.trickl.jackson.module.httpquery.annotations.HttpQuery;
+import com.github.trickl.jackson.module.httpquery.annotations.HttpQueryDelimited;
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import lombok.EqualsAndHashCode;
+import lombok.NoArgsConstructor;
+import lombok.ToString;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+public class EmptyListsTest {
+
+  private static ObjectMapper objectMapper;
+
+  private static final List<String> EXAMPLE_LIST = Arrays.asList("first", "second", "third");
+
+  @BeforeAll
+  public static void setup() {
+    objectMapper = new ObjectMapper();
+    objectMapper.registerModule(new HttpQueryModule());
+  }
+
+  @HttpQuery
+  @NoArgsConstructor
+  @EqualsAndHashCode
+  @ToString
+  private static class RegularListQuery {
+    @JsonProperty("paramA")
+    private List<String> valuesA;
+
+    @JsonProperty("paramB")
+    @JsonInclude(JsonInclude.Include.NON_EMPTY)
+    private List<String> valuesB;
+
+    public RegularListQuery(List<String> valuesA, List<String> valuesB) {
+      this.valuesA = valuesA;
+      this.valuesB = valuesB;
+    }
+  }
+
+  @HttpQuery
+  @NoArgsConstructor
+  @EqualsAndHashCode
+  @ToString
+  private static class DelimitedListQuery {
+    @JsonProperty("paramA")
+    @HttpQueryDelimited
+    private List<String> valuesA;
+
+    @JsonProperty("paramB")
+    @HttpQueryDelimited
+    @JsonInclude(JsonInclude.Include.NON_EMPTY)
+    private List<String> valuesB;
+
+    public DelimitedListQuery(List<String> valuesA, List<String> valuesB) {
+      this.valuesA = valuesA;
+      this.valuesB = valuesB;
+    }
+  }
+
+  @Test
+  public void testRegularListNullIncludedSerialization() throws JsonProcessingException {
+    assertEquals(
+        "?paramA=null&paramB=first&paramB=second&paramB=third",
+        objectMapper.valueToTree(new RegularListQuery(
+            null, EXAMPLE_LIST)).textValue());
+  }
+
+  @Test
+  public void testRegularListNullExcludedSerialization() throws JsonProcessingException {
+    assertEquals(
+        "?paramA=first&paramA=second&paramA=third",
+        objectMapper.valueToTree(new RegularListQuery(EXAMPLE_LIST,
+            null)).textValue());
+  }
+
+  @Test
+  public void testDelimitedListNullIncludedSerialization() throws JsonProcessingException {
+    assertEquals(
+        "?paramA=null&paramB=first%2Csecond%2Cthird",
+        objectMapper.valueToTree(new DelimitedListQuery(
+            null, EXAMPLE_LIST)).textValue());
+  }
+
+  @Test
+  public void testDelimitedListNullExcludedSerialization() throws JsonProcessingException {
+    assertEquals(
+        "?paramA=first%2Csecond%2Cthird",
+        objectMapper.valueToTree(new DelimitedListQuery(EXAMPLE_LIST, 
+            null)).textValue());
+  }
+
+  @Test
+  public void testRegularListEmptyIncludedSerialization() throws JsonProcessingException {
+    assertEquals(
+        "?paramB=first&paramB=second&paramB=third",
+        objectMapper.valueToTree(new RegularListQuery(
+            Collections.emptyList(), EXAMPLE_LIST)).textValue());
+  }
+
+  @Test
+  public void testRegularListEmptyExcludedSerialization() throws JsonProcessingException {
+    assertEquals(
+        "?paramA=first&paramA=second&paramA=third",
+        objectMapper.valueToTree(new RegularListQuery(EXAMPLE_LIST,
+            Collections.emptyList())).textValue());
+  }
+
+  @Test
+  public void testDelimitedListEmptyIncludedSerialization() throws JsonProcessingException {
+    assertEquals(
+        "?paramB=first%2Csecond%2Cthird",
+        objectMapper.valueToTree(new DelimitedListQuery(
+           Collections.emptyList(), EXAMPLE_LIST)).textValue());
+  }
+
+  @Test
+  public void testDelimitedListEmptyExcludedSerialization() throws JsonProcessingException {
+    assertEquals(
+        "?paramA=first%2Csecond%2Cthird",
+        objectMapper.valueToTree(new DelimitedListQuery(EXAMPLE_LIST, 
+           Collections.emptyList())).textValue());
+  }
+}