code: function listenEmpty( handler, isFunction, emitter ){
      const errors = [];
      
      if( isFunction ){
          try {
              handler.call( emitter );
          } catch( error ){
              errors.push( error );
          }
      } else {
          const length = handler.length,
              listeners = handler.slice();
              
          let index = 0;
          
          for( ; index < length; index += 1 ){
              try {
                  listeners[ index ].call( emitter );
              } catch( error ){
                  errors.push( error );
              }
          }
      }
      
      if( errors.length ){
          emitErrors( emitter, errors );
      }
  }
docs: Execute a listener with no arguments.
  @function Emitter~listenEmpty
  @param {EventListener|Array<EventListener>} handler One or more {@link EventListener|listeners} that will be executed on the `emitter`.
  @param {external:boolean} isFunction Whether or not the `handler` is a {@link external:Function|function}.
  @param {Emitter} emitter The emitter.