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.
Unit and integration tests have been failing due to failed logging of
`Error` objects. These were creating an issue where `mocha` was not
properly returning right exit codes, leading to test pipelines
incorrectly passing despite test failures.
- Fix runtime behavior of failing to retrieve error stacks.
- Add tests for error handling.
- Add more robust custom error handling.
Related issues: babel/babel#14273, vuejs/vue-cli#6994.
