ignore setting properties with null values.

As stated in the Feature-Request:

https://github.com/neo4j/neo4j/issues/841

I modified the Primitive.setProperties() method, to fail only when key is null. If the value is null, this property is simply ignored (not set).

With this, a cypher query:

~~~~
CREATE n={myNodePropertyMap}
~~~~

would work even for:

~~~~
Map myNodePropertyMap = new HashMap();
myNode.put("someKey", null);
myNode.put("someOtherProperty", "a value");
~~~~

As a result, a new Node with property "someOtherProperty" is created, but the property "someKey" is ignored.