Catch MRO error when applying missing hints feature.

CONTRIBUTORS.txt

@@ -508,3 +508,5 @@ contributors:
 
 * Maksym Humetskyi (mhumetskyi): contributor
   - Fixed ignored empty functions by similarities checker with "ignore-signatures" option enabled
+
+* Daniel Dorani (doranid): contributor

ChangeLog

@@ -17,6 +17,10 @@ Release date: TBA
 ..
   Put bug fixes that should not wait for a new minor version here
 
+* Fix hard failure when handling missing attribute in a class with duplicated bases
+
+  Closes #4687
+
 * Fix false-positive ``consider-using-with`` (R1732) if a ternary conditional is used together with ``with``
 
   Closes #4676

pylint/checkers/typecheck.py

@@ -185,7 +185,7 @@ def _(node):
 
     try:
         mro = node.mro()[1:]
-    except (NotImplementedError, TypeError):
+    except (NotImplementedError, TypeError, astroid.MroError):
         mro = node.ancestors()
 
     other_values = [value for cls in mro for value in _node_names(cls)]

tests/functional/r/regression/regression_4688_duplicated_bases_member_hints.py

@@ -0,0 +1,7 @@
+# pylint: disable=missing-docstring, pointless-statement, useless-object-inheritance
+# pylint: disable=duplicate-bases, too-few-public-methods
+
+
+class Klass(object, object):
+    def get(self):
+        self._non_existent_attribute # [no-member]

tests/functional/r/regression/regression_4688_duplicated_bases_member_hints.txt

@@ -0,0 +1 @@
+no-member:7:8:Klass.get:Instance of 'Klass' has no '_non_existent_attribute' member:INFERENCE