無法爲Firebase部署雲端功能

我正在部署功能，但後來停止工作，我不知道爲什麼。我已經回覆到示例代碼（from here或here）：無法爲Firebase部署雲端功能

const functions = require('firebase-functions'); 
const admin = require('firebase-admin'); 
admin.initializeApp(functions.config().firebase); 

// Listens for new messages added to /messages/:pushId/original and creates an 
// uppercase version of the message to /messages/:pushId/uppercase 
exports.makeUppercase = functions.database.ref('/messages/{pushId}/original') 
    .onWrite(event => { 
     // Grab the current value of what was written to the Realtime Database. 
     const original = event.data.val(); 
     console.log('Uppercasing', event.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 event.data.ref.parent.child('uppercase').set(uppercase); 
    });

但現在，當我運行firebase deploy --only functions我得到：

=== Deploying to 'mydb'... 

i deploying functions 
i functions: ensuring necessary APIs are enabled... 
i runtimeconfig: ensuring necessary APIs are enabled... 
+ runtimeconfig: all necessary APIs are enabled 
+ functions: all necessary APIs are enabled 
i functions: preparing functions directory for uploading... 
i functions: packaged functions (2.04 KB) for uploading 
! functions: Upload Error: Cannot read property 'response' of undefined 
i starting release process (may take several minutes)... 
i functions: updating function makeUppercase... 
! functions[makeUppercase]: Deploy Error: Function load error: Node.js module defined by file index.js is expected to export function named makeUppercase 
+ functions: 0 function(s) deployed successfully. 


Functions deploy had errors. To continue deploying other features (such as database), run: 
    firebase deploy --except functions 

Error: Functions did not deploy properly.

有什麼不對？

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