Allow proper NoneType conversions when handling nested dataclass members and such.

[JackUrb]

Before:

TypeError: Failed to convert inputs of task 'workflows.subgraphs.geometric_filtering.build_geometric_filtering_outputs':
  Failed argument 'density': Python value cannot be None, expected <class 'NoneType'>/[Flyte Serialized object: Type: 
<LiteralType> Value: <simple: NONE>]

This is pretty nonsensical, upset that the value is None when NoneType is expected.

The fix is pretty simple, and this no longer happens.