firebase functions INVALID_ARGUMENT HTTP error 400 at deploy

trying to solve problem for 5 hours now on firebase realtime database functions, at 'firebase deploy':

never had this until today

function is:

exports.makeUppercase = functions.database.ref('/userfollowers/{pushId}/followers')
    .onWrite((change, context) => {
      // Only edit data when it is first created.
      if (change.before.exists()) {
        return null;
      }
      // Exit when the data is deleted.
      if (!change.after.exists()) {
        return null;
      }
      // Grab the current value of what was written to the Realtime Database.
      const original = change.after.val();
      console.log('Uppercasing', context.params.pushId, original);
      const uppercase = original.toUpperCase();
      // You must return a Promise when performing asynchronous tasks inside a Functions such as
      // writing to the Firebase Realtime Database.
      // Setting an "uppercase" sibling in the Realtime Database returns a Promise.
      return change.after.ref.parent.child('uppercase').set(uppercase);
    });
which is straight out of documentation.

the terminal shows:

⚠  functions: failed to create function makeUppercase
HTTP Error: 400, The request has errors

cloud functions logs show:

{"@type":"type.googleapis.com/google.cloud.audit.AuditLog","status":{"code":3,"message":"INVALID_ARGUMENT"},"authenticationInfo":{"principalEmail":"[email protected]"},"requestMetadata":{"callerIp":"86.120.235.246","callerSuppliedUserAgent":"FirebaseCLI/3.19.0,gzip(gfe),gzip(gfe)","requestAttributes":{"time":"2019-05-14T08:34:18.563Z","auth":{}},"destinationAttributes":{}},"serviceName":"cloudfunctions.googleapis.com","methodName":"google.cloud.functions.v1.CloudFunctionsService.CreateFunction","authorizationInfo":[{"resource":"projects/parkour-9136c/locations/us-central1/functions/makeUppercase","permission":"cloudfunctions.functions.create","granted":true,"resourceAttributes":{}},{"permission":"cloudfunctions.functions.create","granted":true,"resourceAttributes":{}}],"resourceName":"projects/parkour-9136c/locations/us-central1/functions/makeUppercase","request":{"location":"projects/parkour-9136c/locations/us-central1","@type":"type.googleapis.com/google.cloud.functions.v1.CreateFunctionRequest","function":{"labels":{"deployment-tool":"cli-firebase"},"entryPoint":"makeUppercase","eventTrigger":{"eventType":"providers/google.firebase.database/eventTypes/ref.write","resource":"projects/_/instances/parkour-9136c/refs/userfollowers/{pushId}/followers","service":"firebaseio.com"},"sourceUploadUrl":"https://storage.googleapis.com/gcf-upload-us-central1-f5adb7fe-7321-4f3c-8fe0-2b2307d26138/5b099ea8-161b-44a7-a3bd-18ce75c64859.zip?GoogleAccessId=service-807137615499@gcf-admin-robot.iam.gserviceaccount.com&Expires=1557824657&Signature=PJKzJsZtHWO1kIkmrSojpdgvb0jRzV91eNC9rZc4j%2FMcoHjILGm36FKCt6qQ2fxeAUu1%2FbrxpagdI7fHmUUUrDdTmnTNISr7FiN61sifUI%2B%2FGnUwo8SguzvrA7kADFqu8nD05FAo7BvG7biUrHmLgISlwo5dTKqcTSmExnaICA1tHYxjz%2Fk0RbmdGkcQ5HdeCKBnW0R7wQPsxswQyvR4cAU4WD2m3PPM9lncVr7pB%2Fh77FboGLi3sq%2FGHyEwUtjfUmyN9d%2FYUpKs48TMsGPknAGIvaFFUWQR23YCDUcrPipq1nW2W1JUdf5nGylYmVEeyF3jLrm%2BsOIcXiZ6LCRhpg%3D%3D","name":"projects/parkour-9136c/locations/us-central1/functions/makeUppercase"}}}

what is the solution? thanks

https://github.com/firebase/firebase-tools/issues/1317