Ensure NULL-able Enums don't raise peewee.IntegrityError

peewee_plus.py

@@ -367,7 +367,11 @@ class EnumField(peewee.CharField):  # pylint: disable=abstract-method
 
     def python_value(self, value: str) -> enum.Enum:
         try:
-            return self.enumeration[super().python_value(value)]
+            return (
+                None
+                if value is None and self.null
+                else self.enumeration[super().python_value(value)]
+            )
         except KeyError:
             raise peewee.IntegrityError(
                 f"Enum {self.enumeration.__name__} has no value with name '{value}'"