Fixed #19298 -- Added MultiValueField.__deepcopy__

Thanks nick.phillips at otago.ac.nz for the report.

django/forms/fields.py

@@ -977,6 +977,11 @@ class MultiValueField(Field):
                 f.required = False
         self.fields = fields
 
+    def __deepcopy__(self, memo):
+        result = super(MultiValueField, self).__deepcopy__(memo)
+        result.fields = tuple([x.__deepcopy__(memo) for x in self.fields])
+        return result
+
     def validate(self, value):
         pass