pushStack method Null safety

void pushStack()

"lift" stack, after which one can write to x

Implementation

void pushStack() {
  void f(final List<Value>? st) {
    if (st != null) {
      st[3] = st[2];
      st[2] = st[1];
      st[1] = st[0];
    }
  }

  f(_stack);
  f(_imaginaryStack);
  needsSave = true;
  _clxDone = false;
}