Incomming webhooks test failed due to invalid json error

[iamstevetran-zz]

Rocket.Chat Version: 0.54.2
Running Instances: Docker

Reproduce steps:

• Navigate to https://rocketchat.instance/admin/integrations/incoming/
• Enter chanel name: #general
• Enable integration and save
• Copy and run generated test command

Actual result:

• Message returned: Bad request
• Docker logs:

Error: invalid json
  at parse (/app/bundle/programs/server/npm/node_modules/meteor/simple_json-routes/node_modules/connect/node_modules/body-parser/lib/types/json.js:83:15)
  at /app/bundle/programs/server/npm/node_modules/meteor/simple_json-routes/node_modules/connect/node_modules/body-parser/lib/read.js:108:18
  at invokeCallback (/app/bundle/programs/server/npm/node_modules/meteor/simple_json-routes/node_modules/connect/node_modules/body-parser/node_modules/raw-body/index.js:262:16)
  at done (/app/bundle/programs/server/npm/node_modules/meteor/simple_json-routes/node_modules/connect/node_modules/body-parser/node_modules/raw-body/index.js:251:7)
  at IncomingMessage.onEnd (/app/bundle/programs/server/npm/node_modules/meteor/simple_json-routes/node_modules/connect/node_modules/body-parser/node_modules/raw-body/index.js:308:7)
  at emitNone (events.js:67:13)
  at IncomingMessage.emit (events.js:166:7)
  at endReadableNT (_stream_readable.js:923:12)
  at nextTickCallbackWith2Args (node.js:511:9)
  at process._tickDomainCallback (node.js:466:17)