original_string: public function isNotNull($field)
      {
          if (!($field instanceof ExpressionInterface)) {
              $field = new IdentifierExpression($field);
          }
  
          return $this->add(new UnaryExpression('IS NOT NULL', $field, UnaryExpression::POSTFIX));
      }
code: public function isNotNull($field)
      {
          if (!($field instanceof ExpressionInterface)) {
              $field = new IdentifierExpression($field);
          }
  
          return $this->add(new UnaryExpression('IS NOT NULL', $field, UnaryExpression::POSTFIX));
      }
code_tokens: public function isNotNull ( $ field ) { if ( ! ( $ field instanceof ExpressionInterface ) ) { $ field = new IdentifierExpression ( $ field ) ; } return $ this -> add ( new UnaryExpression ( 'IS NOT NULL' , $ field , UnaryExpression :: POSTFIX ) ) ; }
docstring: Adds a new condition to the expression object in the form "field IS NOT NULL".
  
  @param string|\Cake\Database\ExpressionInterface $field database field to be
  tested for not null
  @return $this
docstring_tokens: Adds a new condition to the expression object in the form field IS NOT NULL .