copletion in case of null in dataflow now works, also fixed case with isinstance with tuple (PY-1133)

python/src/com/jetbrains/python/psi/impl/PyQualifiedReferenceImpl.java

@@ -133,7 +133,7 @@ public class PyQualifiedReferenceImpl extends PyReferenceImpl {
     PyExpression qualifier = myElement.getQualifier();
     assert qualifier != null;
 
-    PyType qualifierType = qualifier.getType(TypeEvalContext.variants());
+    PyType qualifierType = qualifier.getType(TypeEvalContext.slow());
     ProcessingContext ctx = new ProcessingContext();
     final Set<String> namesAlready = new HashSet<String>();
     ctx.put(PyType.CTX_NAMES, namesAlready);

python/src/com/jetbrains/python/psi/impl/PyReferenceExpressionImpl.java

@@ -280,7 +280,7 @@ public class PyReferenceExpressionImpl extends PyElementImpl implements PyRefere
           if (defs.length > 0) {
             PyType type = getTypeIfExpr(defs[0], context);
             for (int i = 1; i < defs.length; i++) {
-              type = PyUnionType.union(type, getTypeIfExpr(defs[i], context), context.allowNulls());
+              type = PyUnionType.union(type, getTypeIfExpr(defs[i], context));
             }
             return type;
           }

python/src/com/jetbrains/python/psi/types/PyUnionType.java

@@ -55,19 +55,6 @@ public class PyUnionType implements PyType {
     }, ", ") + ")";
   }
 
-  @Nullable
-  public static PyType union(PyType type1, PyType type2, boolean allowNulls) {
-    if (allowNulls) {
-      if (type1 == null) {
-        return type2;
-      }
-      if (type2 == null) {
-        return type1;
-      }
-    }
-    return union(type1, type2);
-  }
-
   @Nullable
   public static PyType union(PyType type1, PyType type2) {
     if (type1 instanceof PyTupleType && type2 instanceof PyTupleType) {

python/src/com/jetbrains/python/psi/types/TypeEvalContext.java

@@ -11,7 +11,6 @@ import java.util.Map;
  */
 public class TypeEvalContext {
   private boolean myAllowDataFlow;
-  private boolean allowNulls = false;
 
   private Map<PyExpression, PyType> myEvaluated = new HashMap<PyExpression, PyType>();
 
@@ -27,15 +26,6 @@ public class TypeEvalContext {
     return myAllowDataFlow;
   }
 
-
-  public static TypeEvalContext variants() {
-    TypeEvalContext context = slow();
-    context.allowNulls = true;
-    
-    return context;
-  }
-
-
   public static TypeEvalContext slow() {
     return new TypeEvalContext(true);
   }
@@ -53,8 +43,4 @@ public class TypeEvalContext {
     myEvaluated.put(expr, result);
     return result;
   }
-
-  public boolean allowNulls() {
-    return allowNulls;
-  }
 }