Fix relation field unknown target object (#13129)

Fixes https://github.com/twentyhq/twenty/issues/12867

Issue:
when you have a variable `toto` which is: `Record<string, MyType>` and
you do toto['xxx'], this will be typed as `MyType` instead of `MyType |
undefined`

Solutions:
- activate `noUncheckedIndexedAccess` check in tsconfig, this is the
preferred solution but will take time to get there (this raises 600+
errors)
- use a Map: cf https://github.com/twentyhq/twenty/pull/13125/files
- set the type to Partial<Record<string, MyType>>. Drawback is that when
you do Object.values(toto), you'll get `Array<MyType | undefined>`.
Hence why we have to filter these behind


<img width="1512" alt="image"
src="https://github.com/user-attachments/assets/d0a0bfed-c441-4e53-84c2-2da98ccbcf50"
/>

packages/twenty-server/src/engine/metadata-modules/utils/get-object-metadata-map-item-by-name-plural.util.ts

@@ -1,3 +1,5 @@
+import { isDefined } from 'twenty-shared/utils';
+
 import { ObjectMetadataItemWithFieldMaps } from 'src/engine/metadata-modules/types/object-metadata-item-with-field-maps';
 import { ObjectMetadataMaps } from 'src/engine/metadata-modules/types/object-metadata-maps';
 
@@ -5,7 +7,9 @@ export const getObjectMetadataMapItemByNamePlural = (
   objectMetadataMaps: ObjectMetadataMaps,
   namePlural: string,
 ): ObjectMetadataItemWithFieldMaps | undefined => {
-  const objectMetadataItems = Object.values(objectMetadataMaps.byId);
+  const objectMetadataItems = Object.values(objectMetadataMaps.byId).filter(
+    isDefined,
+  );
 
   return objectMetadataItems.find(
     (objectMetadata) => objectMetadata.namePlural === namePlural,

packages/twenty-server/src/engine/metadata-modules/utils/get-object-metadata-map-item-by-name-singular.util.ts

@@ -1,3 +1,5 @@
+import { isNonEmptyString } from '@sniptt/guards';
+
 import { ObjectMetadataItemWithFieldMaps } from 'src/engine/metadata-modules/types/object-metadata-item-with-field-maps';
 import { ObjectMetadataMaps } from 'src/engine/metadata-modules/types/object-metadata-maps';
 
@@ -5,7 +7,11 @@ export const getObjectMetadataMapItemByNameSingular = (
   objectMetadataMaps: ObjectMetadataMaps,
   nameSingular: string,
 ): ObjectMetadataItemWithFieldMaps | undefined => {
-  return objectMetadataMaps.byId[
-    objectMetadataMaps.idByNameSingular[nameSingular]
-  ];
+  const objectMetadataId = objectMetadataMaps.idByNameSingular[nameSingular];
+
+  if (!isNonEmptyString(objectMetadataId)) {
+    return undefined;
+  }
+
+  return objectMetadataMaps.byId[objectMetadataId];
 };

packages/twenty-server/src/engine/metadata-modules/utils/validate-no-other-object-with-same-name-exists-or-throw.util.ts

@@ -1,4 +1,5 @@
 import { t } from '@lingui/core/macro';
+import { isDefined } from 'twenty-shared/utils';
 
 import {
   ObjectMetadataException,
@@ -19,14 +20,16 @@ export const validatesNoOtherObjectWithSameNameExistsOrThrows = ({
   existingObjectMetadataId,
   objectMetadataMaps,
 }: ValidateNoOtherObjectWithSameNameExistsOrThrowsParams) => {
-  const objectAlreadyExists = Object.values(objectMetadataMaps.byId).find(
-    (objectMetadata) =>
-      (objectMetadata.nameSingular === objectMetadataNameSingular ||
-        objectMetadata.namePlural === objectMetadataNamePlural ||
-        objectMetadata.nameSingular === objectMetadataNamePlural ||
-        objectMetadata.namePlural === objectMetadataNameSingular) &&
-      objectMetadata.id !== existingObjectMetadataId,
-  );
+  const objectAlreadyExists = Object.values(objectMetadataMaps.byId)
+    .filter(isDefined)
+    .find(
+      (objectMetadata) =>
+        (objectMetadata.nameSingular === objectMetadataNameSingular ||
+          objectMetadata.namePlural === objectMetadataNamePlural ||
+          objectMetadata.nameSingular === objectMetadataNamePlural ||
+          objectMetadata.namePlural === objectMetadataNameSingular) &&
+        objectMetadata.id !== existingObjectMetadataId,
+    );
 
   if (objectAlreadyExists) {
     throw new ObjectMetadataException(