title: i keep getting Cannot GET / on heroku after deploying my system
body: <p>as the title says i keep getting Cannot GET / after i deployed my system there , so when i type heroku logs i get these 2 errors :
  first</p>
  <pre><code>(node:23) UnhandledPromiseRejectionWarning: MongooseError: The `uri` parameter to `openUri()` must be a string, got &quot;undefined&quot;. Make sure the first parameter to `mongoose.connect()` or `mongoose.createConnection()` is a string.
  </code></pre>
  <p>even tho i fixed my parameter variables for both development and production servers , to connect using mongoose i have process.env.MONGODB in the code and it is working correctly on the development server.</p>
  <p>the second error is</p>
  <pre><code>(node:23) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)    
  </code></pre>
  <p>and it doesnt have a reference to the specific code or line or file to know where the mistake is exactly</p>
  <p>and these are my Dependencies for the system</p>
  <pre><code>{
   &quot;name&quot;: &quot;task-manager&quot;,
   &quot;version&quot;: &quot;1.0.0&quot;,
   &quot;description&quot;: &quot;&quot;,
   &quot;main&quot;: &quot;index.js&quot;,
   &quot;scripts&quot;: {
     &quot;start&quot;: &quot;node src/app.js&quot;,
     &quot;dev&quot;: &quot;env-cmd -f ./config/dev.env nodemon src/app.js&quot;
   },
   &quot;keywords&quot;: [],
   &quot;author&quot;: &quot;&quot;,
   &quot;license&quot;: &quot;ISC&quot;,
   &quot;dependencies&quot;: {
     &quot;@sendgrid/mail&quot;: &quot;^7.3.0&quot;,
     &quot;bcryptjs&quot;: &quot;^2.4.3&quot;,
     &quot;express&quot;: &quot;^4.17.1&quot;,
     &quot;jsonwebtoken&quot;: &quot;^8.5.1&quot;,
     &quot;mongodb&quot;: &quot;^3.6.2&quot;,
     &quot;mongoose&quot;: &quot;^5.10.9&quot;,
     &quot;multer&quot;: &quot;^1.4.2&quot;,
     &quot;sharp&quot;: &quot;^0.26.2&quot;,
     &quot;validator&quot;: &quot;^13.1.17&quot;
   },
   &quot;devDependencies&quot;: {
     &quot;env-cmd&quot;: &quot;^10.1.0&quot;,
     &quot;nodemon&quot;: &quot;^2.0.5&quot;
   }
  </code></pre>
  <p>}</p>