code: function _fnConvert(filters) {
                  var _iF, _lenF, _keysF,
                      _filter,
                      _state;
  
                  // convert filter object to array filter
                  if (angular.isObject(filters) && !angular.isArray(filters)) {
                      _keysF  = Object.keys(filters);
                      _lenF   = _keysF.length;
                      _filter = [];
  
                      if (_lenF > 0) {
                          for (_iF = 0; _iF < _lenF; _iF++) {
  
                              if (typeof filters[_keysF[_iF]] === 'string' && filters[_keysF[_iF]].length === 0) {
                                  continue;
                              } else if (angular.isArray(filters[_keysF[_iF]])) {
                                  _state = filters[_keysF[_iF]];
                              } else if (angular.isObject(filters[_keysF[_iF]])) {
                                  _state = _fnConvert(filters[_keysF[_iF]]);
                              } else {
                                  _state = {
                                      field:    _keysF[_iF],
                                      callback: filters[_keysF[_iF]]
                                  };
                              }
                              _filter.push(_state);
                          }
                      }
  
                      return _filter;
                  }
                  else {
                      return filters;
                  }
              }
docs: `_fnConvert` to convert `filter` `object` to `array` invaild.
  
  @param {object|array} filters
  @returns {array} Instead of `filter` or new array invaild *(converted from filter)*
  @private