@Override
  protected void doFlush(@NotNull DfaVariableValue var, boolean markFlushed) {
    if (getDfType(var) == DfTypes.NULL) {
      myStack.replaceAll(val -> val == var ? getFactory().fromDfType(DfTypes.NULL) : val);
    }
    super.doFlush(var, markFlushed);
  }
@Override
  protected void doFlush(@NotNull DfaVariableValue var, boolean markFlushed)