system/Database/Schema/ColumnDefination.php
/**
     * Allow NULL values to be inserted into the column
     *
     * @return $this
     */
Allow NULL values to be inserted into the column
@return $this
Allow NULL values to be inserted into the column @return $this
public function nullable()
    {
        self::$migration = substr(self::$migration, 0, strlen(self::$migration) - 10);
        self::$migration .= " NULL, ";
        $this->is_null = true;
        return $this;
    }
public function nullable ( ) { self :: $ migration = substr ( self :: $ migration , 0 , strlen ( self :: $ migration ) - 10 ) ; self :: $ migration .= "  NULL,  " ; $ this -> is_null = true ; return $ this ; }
Allow NULL values to be inserted into the column
 @return $this
Allow NULL values to be inserted into the column @return $this