Refactor to enforce strictNullChecks

This commit applies `strictNullChecks` to the entire codebase to improve
maintainability and type safety. Key changes include:

- Remove some explicit null-checks where unnecessary.
- Add necessary null-checks.
- Refactor static factory functions for a more functional approach.
- Improve some test names and contexts for better debugging.
- Add unit tests for any additional logic introduced.
- Refactor `createPositionFromRegexFullMatch` to its own function as the
  logic is reused.
- Prefer `find` prefix on functions that may return `undefined` and
  `get` prefix for those that always return a value.

tests/unit/shared/Stubs/CategoryCollectionParserStub.ts

@@ -24,10 +24,11 @@ export class CategoryCollectionParserStub {
   }
 
   public getStub(): CategoryCollectionParserType {
-    return (data: CollectionData, info: IProjectInformation) => {
+    return (data: CollectionData, info: IProjectInformation): ICategoryCollection => {
       this.arguments.push({ data, info });
-      if (this.returnValues.has(data)) {
-        return this.returnValues.get(data);
+      const foundReturnValue = this.returnValues.get(data);
+      if (foundReturnValue) {
+        return foundReturnValue;
       }
       // Get next OS with a unique OS so mock does not result in an invalid app due to duplicated OS
       // collections.