MissingEnvVarsError: The following variables were defined in .env.example but are not present in the environment:

[knav33n]

Thanks for that great course, got to learn quite a lot.
Should we configure these env variables in dokku while deploying?

App container failed to start!!
       /usr/src/app/node_modules/dotenv-safe/index.js:31
                   throw new MissingEnvVarsError(allowEmptyValues, options.path || '.env', example, missing, dotenvResult.error);
                   ^
       MissingEnvVarsError: The following variables were defined in .env.example but are not present in the environment:
         DATABASE_URL
       Make sure to add them to .env or directly to the environment.
       If you expect any of these variables to be empty, you can use the allowEmptyValues option:
       require('dotenv-safe').config({
         allowEmptyValues: true
       });
           at Object.config (/usr/src/app/node_modules/dotenv-safe/index.js:31:19)
           at /usr/src/app/node_modules/dotenv-safe/config.js:9:18
           at Object.<anonymous> (/usr/src/app/node_modules/dotenv-safe/config.js:10:3)
           at Module._compile (internal/modules/cjs/loader.js:1076:30)
           at Object.Module._extensions..js (internal/modules/cjs/loader.js:1097:10)
           at Module.load (internal/modules/cjs/loader.js:941:32)
           at Function.Module._load (internal/modules/cjs/loader.js:782:14)
           at Module.require (internal/modules/cjs/loader.js:965:19)
           at require (internal/modules/cjs/helpers.js:88:18)
           at Object.<anonymous> (/usr/src/app/dist/index.js:18:1) {
         missing: [ 'DATABASE_URL' ],
         sample: '.env.example',
         example: '.env.example'
       }

[benawad]

DATABASE_URL comes from linking dokku postgres instance