Fix dict.__missing__

Author: msimacek

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/dict/DictBuiltins.java

@@ -68,7 +68,6 @@
 import com.oracle.graal.python.builtins.objects.function.PKeyword;
 import com.oracle.graal.python.builtins.objects.mappingproxy.PMappingproxy;
 import com.oracle.graal.python.builtins.objects.method.PBuiltinMethod;
-import com.oracle.graal.python.builtins.objects.method.PMethod;
 import com.oracle.graal.python.builtins.objects.object.PythonObjectLibrary;
 import com.oracle.graal.python.builtins.objects.str.PString;
 import com.oracle.graal.python.builtins.objects.tuple.PTuple;
@@ -340,8 +339,7 @@ protected Object misssing(VirtualFrame frame, Object self, Object key,
         }
 
         protected boolean hasMissing(Object self, PythonObjectLibrary lib) {
-            Object missing = lib.lookupAttributeOnType(self, __MISSING__);
-            return missing != PNone.NO_VALUE && missing instanceof PMethod;
+            return lib.lookupAttributeOnType(self, __MISSING__) != NO_VALUE;
         }
     }