code: function arrayToObject ( keyPath, arr ) {
      var res = {}, key, element;
  
      for ( var i = 0, len = arr.length; i < len; i++ ) {
          element = arr[ i ];
          key     = getOrNull( element, keyPath );
          if ( key ) res[ key ] = element;
      }
      
      return res;
  }
docs: Converts array to object, using `keyPath`
  for building unique keys.
  @param {(String|Array)} keyPath - path to `key` value
  in the array element.
  @param {Object[]} - array to convert.
  @return {Object}