Possible band-aid fix for https://github.com/python/mypy/issues/4581

fix.diff

diff --git a/mypy/checker.py b/mypy/checker.py
index 7b0180f79..488ae825f 100644
--- a/mypy/checker.py
+++ b/mypy/checker.py
@@ -991,9 +991,11 @@ class TypeChecker(NodeVisitor[None], CheckerPluginInterface):
 
                 if is_unsafe_overlapping_signatures(forward_tweaked,
                                                     reverse_tweaked):
+                    rev_name = reverse_class.name() if reverse_class is not None else None
+                    fwd_name = forward_base.type.name() if forward_base and hasattr(forward_base, 'type ') and forward_base.type else None
                     self.msg.operator_method_signatures_overlap(
-                        reverse_class.name(), reverse_name,
-                        forward_base.type.name(), forward_name, context)
+                        rev_name, reverse_name,
+                        fwd_name, forward_name, context)
             elif isinstance(forward_item, Overloaded):
                 for item in forward_item.items():
                     self.check_overlapping_op_methods(
diff --git a/mypy/messages.py b/mypy/messages.py
index 3edc1fee9..57ae30082 100644
--- a/mypy/messages.py
+++ b/mypy/messages.py
@@ -934,10 +934,12 @@ class MessageBuilder:
     def operator_method_signatures_overlap(
             self, reverse_class: str, reverse_method: str, forward_class: str,
             forward_method: str, context: Context) -> None:
-        self.fail('Signatures of "{}" of "{}" and "{}" of "{}" '
+        rev_class_msg = ' of "{}"'.format(reverse_class) if reverse_class else ""
+        fwd_class_msg = ' of "{}"'.format(forward_class) if forward_class else ""
+        self.fail('Signatures of "{}"{} and "{}"{} '
                   'are unsafely overlapping'.format(
-                      reverse_method, reverse_class,
-                      forward_method, forward_class),
+                      reverse_method, rev_class_msg,
+                      forward_method, fwd_class_msg),
                   context)
 
     def forward_operator_not_callable(