code: function (signalName) {
  
        var evt = this._event_find('WorkflowExecutionSignaled', 'signalName', signalName);
        if(!evt) {
          return null;
        }
  
        var signalInput = evt.workflowExecutionSignaledEventAttributes.input;
        try {
          var d = JSON.parse(signalInput);
          return d;
        } catch (ex) {
          return signalInput;
        }
     }
docs: Returns the signal input or null if the signal is not found or doesn't have JSON input
  @param {String} signalName
  @returns {Mixed}