Do not explicitly add the mutator to the module. Setting the Mutator.module property is sufficient, and prevents from a duplicate one from being added with a None key.

eos/saveddata/module.py

@@ -164,8 +164,9 @@ class Module(HandledItem, HandledCharge, ItemAttrShortcut, ChargeAttrShortcut):
             if self.__baseItem:
                 for x in self.mutaplasmid.attributes:
                     attr = self.item.attributes[x.name]
-                    if attr.ID not in self.mutators:  # create the mutator
-                        self.mutators[attr.ID] = Mutator(self, attr, attr.value)
+                    id = attr.ID
+                    if id not in self.mutators:  # create the mutator
+                        Mutator(self, attr, attr.value)
                 # @todo: remove attributes that are no longer part of the mutaplasmid.
 
             self.__itemModifiedAttributes.mutators = self.mutators

eos/saveddata/mutator.py

@@ -41,9 +41,13 @@ class Mutator(EqBase):
     """
 
     def __init__(self, module, attr, value):
+        # this needs to be above module assignment, as assigning the module will add it to the list and it via
+        # relationship and needs this set 4correctly
+        self.attrID = attr.ID
+
         self.module = module
         self.moduleID = module.ID
-        self.attrID = attr.ID
+
         self.__attr = attr
         self.build()
         self.value = value  # must run after the build(), because the validator requires build() to run first