Let ConvertRepresentationStep ignore unspecified result properties

nerdd_module/model/convert_representations_step.py

@@ -12,13 +12,17 @@ def __init__(
         self, result_properties: List[ResultProperty], output_format: str, **kwargs: Any
     ) -> None:
         super().__init__()
+        self._result_properties = result_properties
         self._converter_map = {
             p.name: Converter.get_converter(p, output_format, **kwargs) for p in result_properties
         }
 
     def _process(self, record: dict) -> dict:
         result = {
-            k: self._converter_map[k].convert(input=v, context=record) for k, v in record.items()
+            k.name: self._converter_map[k.name].convert(
+                input=record.get(k.name, None), context=record
+            )
+            for k in self._result_properties
         }
 
         return {k: v for k, v in result.items() if v is not Converter.HIDE}