code: protected function phpTypecastValue($value)
      {
          if ($value === null) {
              return null;
          }
  
          switch ($this->type) {
              case Schema::TYPE_BOOLEAN:
                  switch (strtolower($value)) {
                      case 't':
                      case 'true':
                          return true;
                      case 'f':
                      case 'false':
                          return false;
                  }
                  return (bool) $value;
              case Schema::TYPE_JSON:
                  return $this->disableJsonSupport ? $value : json_decode($value, true);
          }
  
          return parent::phpTypecast($value);
      }
docs: Casts $value after retrieving from the DBMS to PHP representation.
  
  @param string|null $value
  @return bool|mixed|null