Deployment failed : threadsafe is a required field

while using [Push-to-Deploy](https://cloud.google.com/tools/repo/push-to-deploy) Error message : "Deployment failed. Details: Deployment failed, details: { Failed to load application, threadsafe is a required field., none}"

i am using google git with "Build with and run tests :Deploy source only (Python, PHP)" no billing with netbean IDE to push my hello world code ([link to google tutorial](https://cloud.google.com/appengine/docs/php/gettingstarted/helloworld)) there but failed after adding threadsafe solved my problem