Not able to invoke Launch Request from test simulator

Even though the lambda function is having LaunchRequest defined. invocations in the format "open ", "launch ", "start " from alexa skill simulator is not giving any response at all. Skill I/O json input is also not shown. Please refer to the attachment.

Launch request was tested from lambda function and was successfully executed.

The reason for no response was invocation error at lambda. Lambda logs show the following:

“errorMessage”: “One or more parameter values were invalid: An AttributeValue may not contain an empty string”,

I am trying to solve this.