diff --git a/README.md b/README.md
index 0f31bb9..732de0e 100644
--- a/README.md
+++ b/README.md
@@ -11,9 +11,9 @@ The library is built specifically for converting data into a [neo4j](https://neo
 
 Note: The [py2neo](https://py2neo.org/2021.1/index.html) library does not support parallel relations of the same type (same source, same target and same type). If your graph requires such parallel relations please checkout the provided [py2neo extensions](/docs/documentation.md#py2neo-extensions).
 ## Installation
-If you have setup a private ssh key for your github, copy-paste the command below to install the latest version ([v0.4.4][latest_tag]):
+If you have setup a private ssh key for your github, copy-paste the command below to install the latest version ([v0.4.5][latest_tag]):
 ```
-$ pip install git+ssh://git@github.com/sg-dev/rel2graph@v0.4.4
+$ pip install git+ssh://git@github.com/sg-dev/rel2graph@v0.4.5
 ```
 
 If you don't have ssh set up, download the latest wheel [here][latest_wheel] and install the wheel with:
@@ -85,7 +85,7 @@ converter()
 # Known issues
 If you encounter a bug or an unexplainable behavior, please check the [known issues](https://github.com/sg-dev/rel2graph/labels/bug) list. If your issue is not found, submit a new one.
 
-[latest_version]: v0.4.4
-[latest_tag]: https://github.com/sg-dev/rel2graph/releases/tag/v0.4.4
-[latest_wheel]: https://github.com/sg-dev/rel2graph/releases/download/v0.4.4/rel2graph-0.4.4-py3-none-any.whl
+[latest_version]: v0.4.5
+[latest_tag]: https://github.com/sg-dev/rel2graph/releases/tag/v0.4.5
+[latest_wheel]: https://github.com/sg-dev/rel2graph/releases/download/v0.4.5/rel2graph-0.4.5-py3-none-any.whl
 [wiki]: docs/documentation.md
diff --git a/rel2graph/core/graph_elements.py b/rel2graph/core/graph_elements.py
index 57d6114..2e9526f 100644
--- a/rel2graph/core/graph_elements.py
+++ b/rel2graph/core/graph_elements.py
@@ -60,7 +60,7 @@ def key(self):
     def value(self):
         """Any value that is allowed in the graph (String, Int, Float, Bool)"""
         # If the value is not allowed in neo4j it is converted to strings
-        if not isinstance(self._value, (numbers.Number, str, bool, date, datetime)):
+        if not self._value is None and not isinstance(self._value, (numbers.Number, str, bool, date, datetime)):
             return str(self._value)
         return self._value
 
diff --git a/setup.py b/setup.py
index f7bdf6b..7715efa 100644
--- a/setup.py
+++ b/setup.py
@@ -9,7 +9,7 @@
 setup(
     name = "rel2graph", 
     packages = find_packages(),
-    version = "0.4.4",
+    version = "0.4.5",
     description = "Library for converting relational data into graph data (neo4j)",
     author = "Julian Minder",
     author_email = "jminder@ethz.ch",