anchor.diff:      UnknownTypes;
   find_unknown_types_helper(reference, _TypeInfo, UnknownTypes) ->
       UnknownTypes;
  +find_unknown_types_helper(none, _TypeInfo, UnknownTypes) ->
  +    UnknownTypes;
   find_unknown_types_helper(nil, _TypeInfo, UnknownTypes) ->
       UnknownTypes;
   find_unknown_types_helper(node, _TypeInfo, UnknownTypes) ->
  
positive.code:     nil;
  parse_type({type, _Line, node, []}, _Module) ->
      node;
  parse_type({type, _Line, reference, []}, _Module) ->
      reference;
  parse_type({type, _Line, term, []}, _Module) ->
  
negative.code:     | pid
      | port
      | reference
      | none
      | {typedef, module(), atom()}
      | atom
      | float
  