Getting null value onDelete() in Firebase cloud function

I am getting null value in onDelete() firebase cloud function. Below is my code

 exports.jobSeekerToES=functions.database.ref('/Users/{userId}/userFileDetails/files/{fileKey}').onDelete(event=>
{

var file=event.data.val();
console.log("deleted file key"+event.params.fileKey);
console.log("deleted file "+file);  // file is null

});

it prints fileKey on logs. But file is null Please help me where i am wrong