Strapi Can not start server with Cannot read properties of undefined (reading ‘toLowerCase’)

 I encounter this error while building a backend app with Strapi.io

--------------------------------------

$ strapi develop

✔ Cleaning dist dir (8ms)

⠋ Building build context

[INFO] Including the following ENV variables as part of the JS bundle:

- ADMIN_PATH

- STRAPI_ADMIN_BACKEND_URL

- STRAPI_TELEMETRY_DISABLED

✔ Building build context (138ms)

✔ Creating admin (7498ms)

⠸ Loading Strapi[ERROR] There seems to be an unexpected error, try again with --debug for more information

┌────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐│ ││ TypeError: Cannot read properties of undefined (reading 'toLowerCase') ││ at Function.singular (/Users/yj/projects/apis/apis-strapi/node_modules/pluralize/pluralize.js:136:24) ││ at getTypeName ││ (/Users/yj/projects/apis/apis-strapi/node_modules/@strapi/plugin-graphql/dist/server/index.js:873:79) ││ at getEntityName ││ (/Users/yj/projects/apis/apis-strapi/node_modules/@strapi/plugin-graphql/dist/server/index.js:877:15) ││ at Object.getEntityResponseName ││ (/Users/yj/projects/apis/apis-strapi/node_modules/@strapi/plugin-graphql/dist/server/index.js:883:15) ││ at addRegularRelationalAttribute ││ (/Users/yj/projects/apis/apis-strapi/node_modules/@strapi/plugin-graphql/dist/server/index.js:1575:108) ││ at /Users/yj/projects/apis/apis-strapi/node_modules/@strapi/plugin-graphql/dist/server/index.js:1644:15 ││ at Array.forEach (<anonymous>) ││ at Object.definition ││ (/Users/yj/projects/apis/apis-strapi/node_modules/@strapi/plugin-graphql/dist/server/index.js:1618:96) ││ at SchemaBuilder.walkOutputType ││ (/Users/yj/projects/apis/apis-strapi/node_modules/nexus/dist/builder.js:1030:13) ││ at SchemaBuilder.walkTypes (/Users/yj/projects/apis/apis-strapi/node_modules/nexus/dist/builder.js:308:26) ││ │└────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

✨ Done in 12.96s.

 

This happens when

You have a field you've added to one of your Collection Type that has missing Collection relationships.

For my case, I've added a new field to Users Collection in 

user-permissions/content-type/user/schema.json 

it has one of entities

"phone": {

"type": "relation",

"relation": "oneToOne",

"target": "api::phone.phone",

"mappedBy": "creator"

}

and that phone Collection is missing

Once you delete the phone field from user, it works just fine

Cheers