/**
* Negates an expression for the current field.
*
* You can create a new expression using the {@link Builder::expr()} method.
*
* @see Expr::not()
* @see http://docs.mongodb.org/manual/reference/operator/not/
* @param array|Expr $expression
* @return self
*/
public function not($expression)
{
$this->expr->not($expression);
return $this;
}