feat(graphql): improve non-nullability in query result types (#11952)

### What?
Makes several fields and list item types in query results (e.g. `docs`)
non-nullable.

### Why?
When dealing with code generated from a Payload GraphQL schema, it is
often necessary to use type guards and optional chaining.

For example:

```graphql
type Posts {
  docs: [Post]
  ...
}
```

This implies that the `docs` field itself is nullable and that the array
can contain nulls. In reality, neither of these is true. But because of
the types generated by tools like `graphql-code-generator`, the way to
access `posts` ends up something like this:

```ts
const posts = (query.data.docs ?? []).filter(doc => doc != null);
```

Instead, we would like the schema to be:

```graphql
type Posts {
  docs: [Post!]!
  ...
}
```


### How?
The proposed change involves adding `GraphQLNonNull` where appropriate.

---------

Co-authored-by: Dan Ribbens <dan.ribbens@gmail.com>

packages/graphql/src/schema/buildPaginatedListType.ts

@@ -1,21 +1,21 @@
-import { GraphQLBoolean, GraphQLInt, GraphQLList, GraphQLObjectType } from 'graphql'
+import { GraphQLBoolean, GraphQLInt, GraphQLList, GraphQLNonNull, GraphQLObjectType } from 'graphql'
 
 export const buildPaginatedListType = (name, docType) =>
   new GraphQLObjectType({
     name,
     fields: {
       docs: {
-        type: new GraphQLList(docType),
+        type: new GraphQLNonNull(new GraphQLList(new GraphQLNonNull(docType))),
       },
-      hasNextPage: { type: GraphQLBoolean },
-      hasPrevPage: { type: GraphQLBoolean },
-      limit: { type: GraphQLInt },
-      nextPage: { type: GraphQLInt },
+      hasNextPage: { type: new GraphQLNonNull(GraphQLBoolean) },
+      hasPrevPage: { type: new GraphQLNonNull(GraphQLBoolean) },
+      limit: { type: new GraphQLNonNull(GraphQLInt) },
+      nextPage: { type: new GraphQLNonNull(GraphQLInt) },
       offset: { type: GraphQLInt },
-      page: { type: GraphQLInt },
-      pagingCounter: { type: GraphQLInt },
-      prevPage: { type: GraphQLInt },
-      totalDocs: { type: GraphQLInt },
-      totalPages: { type: GraphQLInt },
+      page: { type: new GraphQLNonNull(GraphQLInt) },
+      pagingCounter: { type: new GraphQLNonNull(GraphQLInt) },
+      prevPage: { type: new GraphQLNonNull(GraphQLInt) },
+      totalDocs: { type: new GraphQLNonNull(GraphQLInt) },
+      totalPages: { type: new GraphQLNonNull(GraphQLInt) },
     },
   })

packages/graphql/src/schema/fieldToSchemaMap.ts

@@ -348,11 +348,15 @@ export const fieldToSchemaMap: FieldToSchemaMap = {
         name: joinName,
         fields: {
           docs: {
-            type: Array.isArray(field.collection)
-              ? GraphQLJSON
-              : new GraphQLList(graphqlResult.collections[field.collection].graphQL.type),
+            type: new GraphQLNonNull(
+              Array.isArray(field.collection)
+                ? GraphQLJSON
+                : new GraphQLList(
+                    new GraphQLNonNull(graphqlResult.collections[field.collection].graphQL.type),
+                  ),
+            ),
           },
-          hasNextPage: { type: GraphQLBoolean },
+          hasNextPage: { type: new GraphQLNonNull(GraphQLBoolean) },
         },
       }),
       args: {
@@ -428,7 +432,7 @@ export const fieldToSchemaMap: FieldToSchemaMap = {
       ...objectTypeConfig,
       [formatName(field.name)]: formattedNameResolver({
         type: withNullableType({
-          type: field?.hasMany === true ? new GraphQLList(type) : type,
+          type: field?.hasMany === true ? new GraphQLList(new GraphQLNonNull(type)) : type,
           field,
           forceNullable,
           parentIsLocalized,
@@ -856,7 +860,10 @@ export const fieldToSchemaMap: FieldToSchemaMap = {
     ...objectTypeConfig,
     [formatName(field.name)]: formattedNameResolver({
       type: withNullableType({
-        type: field.hasMany === true ? new GraphQLList(GraphQLString) : GraphQLString,
+        type:
+          field.hasMany === true
+            ? new GraphQLList(new GraphQLNonNull(GraphQLString))
+            : GraphQLString,
         field,
         forceNullable,
         parentIsLocalized,