Remove null objects from list in _without_empty_object

[Wauplin]

I detected a new bug when working on the tag attribute. At the moment, the behavior of _without_empty_object is as follow :

• if a list is empty : return None
• if a list has an object that is empty : return the list with a None inside I think the behavior would be to remove the item from the list, otherwise it creates a List that is not consistent.

My use case :

code = r4.Coding() # No error since all fields are optional
meta = r4.Meta(tag=[code]) 
meta.dict() # Throws an error instead of an empty dictionnary

[codecov[bot]]

Codecov Report

Merging #57 into master will increase coverage by 0.01%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #57      +/-   ##
==========================================
+ Coverage   82.88%   82.89%   +0.01%     
==========================================
  Files          11       11              
  Lines        1291     1292       +1     
==========================================
+ Hits         1070     1071       +1     
  Misses        221      221              

Flag	Coverage Δ
#unittests	82.89% <100.00%> (+0.01%)	:arrow_up:

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Impacted Files	Coverage Δ
...ators/python_pydantic/templates/resource_header.py	98.70% <100.00%> (+0.01%)	:arrow_up:

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