public int GetHashCode(ParameterExpression variable)
 => AwaitExpression.IsAwaiterHolder(variable) ? variable.Type.GetHashCode() : variable.GetHashCode();
 public bool Equals(ParameterExpression x, ParameterExpression y)
 => AwaitExpression.IsAwaiterHolder(x) && AwaitExpression.IsAwaiterHolder(y) ? x?.Type == y?.Type : object.Equals(x, y);