express-session error message

backend     | > wingslikeeagles@0.0.1 start /home/node/app
backend     | > PORT=3001 node index.js
backend     |
backend     | internal/modules/cjs/loader.js:638
backend     |     throw err;
backend     |     ^
backend     |
backend     | Error: Cannot find module 'express-session'
backend     |     at Function.Module._resolveFilename (internal/modules/cjs/loader.js:636:15)
backend     |     at Function.Module._load (internal/modules/cjs/loader.js:562:25)
backend     |     at Module.require (internal/modules/cjs/loader.js:692:17)
backend     |     at require (internal/modules/cjs/helpers.js:25:18)
backend     |     at Object.<anonymous> (/home/node/app/index.js:3:15)
backend     |     at Module._compile (internal/modules/cjs/loader.js:778:30)
backend     |     at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
backend     |     at Module.load (internal/modules/cjs/loader.js:653:32)
backend     |     at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
backend     |     at Function.Module._load (internal/modules/cjs/loader.js:585:3)
backend     | npm ERR! code ELIFECYCLE
backend     | npm ERR! errno 1
backend     | npm ERR! wingslikeeagles@0.0.1 start: `PORT=3001 node index.js`
backend     | npm ERR! Exit status 1
backend     | npm ERR!
backend     | npm ERR! Failed at the wingslikeeagles@0.0.1 start script.
backend     | npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
backend     |
backend     | npm ERR! A complete log of this run can be found in:
backend     | npm ERR!     /home/node/.npm/_logs/2019-09-20T04_20_18_740Z-debug.log
backend exited with code 1