Fixed exception inheritance inspection for unresolved base classes of exceptions (PY-5811)

python/src/com/jetbrains/python/inspections/PyExceptionInheritInspection.java

@@ -49,7 +49,7 @@ public class PyExceptionInheritInspection extends PyInspection {
             PyClass aClass = (PyClass) psiElement;
             for (PyClassRef pyClass : aClass.iterateAncestors()) {
               final String name = pyClass.getClassName();
-              if ("BaseException".equals(name) || "Exception".equals(name)) {
+              if (name == null || "BaseException".equals(name) || "Exception".equals(name)) {
                 return;
               }
             }

python/testData/inspections/PyExceptionInheritInspection/test.py

@@ -10,4 +10,12 @@ def test_basic():
     class D(C, Exception):
       pass
 
-    raise D()
+    raise D()
+
+
+# PY-5811
+def test_unknown_type_exception():
+    Unknown = None
+    class C(Unknown): pass
+
+    raise C()