we're only insertable if it doesn't exist, yet

Author: timfel

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/runtime/interop/PythonMessageResolution.java

@@ -667,12 +667,12 @@ public int access(Object object, Object fieldName) {
                     }
                 }
 
-                if (!isImmutable.execute(owner)) {
-                    info |= KeyInfo.REMOVABLE;
-                    info |= KeyInfo.MODIFIABLE;
-                }
-
-                if (!isImmutable.execute(object)) {
+                if (attr != PNone.NO_VALUE) {
+                    if (!isImmutable.execute(owner)) {
+                        info |= KeyInfo.REMOVABLE;
+                        info |= KeyInfo.MODIFIABLE;
+                    }
+                } else if (!isImmutable.execute(object)) {
                     info |= KeyInfo.INSERTABLE;
                 }