Review

ObjectType.getImplicitPrototype() may return null.

Check result for null before using.

• missing/condition/null_check

com/google/javascript/jscomp/TypeCheck.java

checkInterfaceConflictProperties(NodeTraversal, Node, String, HashMap, HashMap, ObjectType)

class TypeCheck {
  /**
   * Check whether there's any property conflict for for a particular super
   * interface
   * @param t The node traversal object that supplies context
   * @param n The node being visited
   * @param functionName The function name being checked
   * @param properties The property names in the super interfaces that have
   * been visited
   * @param currentProperties The property names in the super interface
   * that have been visited
   * @param interfaceType The super interface that is being visited
   */
  private void checkInterfaceConflictProperties(NodeTraversal t, Node n,
      String functionName, HashMap<String, ObjectType> properties,
      HashMap<String, ObjectType> currentProperties,
      ObjectType interfaceType) {
    Set<String> currentPropertyNames =
        interfaceType.getImplicitPrototype().getOwnPropertyNames();
    for (String name : currentPropertyNames) {
      ObjectType oType = properties.get(name);
      if (oType != null) {
        if (!interfaceType.getPropertyType(name).isEquivalentTo(
            oType.getPropertyType(name))) {
          compiler.report(
              t.makeError(n, INCOMPATIBLE_EXTENDED_PROPERTY_TYPE,
                  functionName, name, oType.toString(),
                  interfaceType.toString()));
        }
      }
      currentProperties.put(name, interfaceType);
    }
    for (ObjectType iType : interfaceType.getCtorExtendedInterfaces()) {
      checkInterfaceConflictProperties(t, n, functionName, properties,
          currentProperties, iType);
    }
  }

}

class CheckNull {
  void pattern(ObjectType interfaceType) {
    ObjectType implicitProto = interfaceType.getImplicitPrototype();
    if (implicitProto != null) {
      implicitProto.getOwnPropertyNames();
    }
  }
}