Introduce class parameter to be able to control the omit none functio…

…nality easily #71

src/omi/dialects/oep/compiler.py

@@ -17,8 +17,9 @@ def compile_date_or_none(x, format=None):
 
 class JSONCompiler(Compiler):
     __METADATA_VERSION = "OEP-1.4.0"
+    OMIT_NONE_FIELDS = False
 
-    def _construct_dict(self, *args, omit_none=False, **kwargs):
+    def _construct_dict(self, *args, omit_none=None, **kwargs):
         """
         Accepts a list of arguments of shape (name: str, field: Compileable) and returns a dictionary that maps
         name -> self.visit(field). If `omit_none` is true, fields that are `None` are ignored.
@@ -32,6 +33,7 @@ def _construct_dict(self, *args, omit_none=False, **kwargs):
         -------
 
         """
+        omit_none = self.OMIT_NONE_FIELDS
         d = {
             field_name: self.visit(field)
             for field_name, field in args