code: private JSType getJSType(Node n) {
      JSType type = n.getJSType();
      if (type == null) {
        // TODO(bradfordcsmith): This branch indicates a compiler bug. It should throw an exception.
        return compiler.getTypeRegistry().getNativeType(JSTypeNative.UNKNOWN_TYPE);
      } else {
        return type;
      }
    }
docs: This method gets the JSType from the Node argument and verifies that it is
  present.