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/application/Parser/Script/Compiler/Expressions/Parser/CompositeExpressionParser.spec.ts

@@ -3,29 +3,20 @@ import { IExpression } from '@/application/Parser/Script/Compiler/Expressions/Ex
 import { IExpressionParser } from '@/application/Parser/Script/Compiler/Expressions/Parser/IExpressionParser';
 import { CompositeExpressionParser } from '@/application/Parser/Script/Compiler/Expressions/Parser/CompositeExpressionParser';
 import { ExpressionStub } from '@tests/unit/shared/Stubs/ExpressionStub';
-import { itEachAbsentObjectValue } from '@tests/unit/shared/TestCases/AbsentTests';
+import { itEachAbsentCollectionValue } from '@tests/unit/shared/TestCases/AbsentTests';
 
 describe('CompositeExpressionParser', () => {
   describe('ctor', () => {
-    it('throws if null parsers given', () => {
-      // arrange
-      const expectedError = 'missing leafs';
-      const parsers = null;
-      // act
-      const act = () => new CompositeExpressionParser(parsers);
-      // assert
-      expect(act).to.throw(expectedError);
-    });
-    describe('throws if one of the parsers is undefined', () => {
-      itEachAbsentObjectValue((absentValue) => {
+    describe('throws when parsers are missing', () => {
+      itEachAbsentCollectionValue<IExpressionParser>((absentCollection) => {
         // arrange
-        const expectedError = 'missing leaf';
-        const parsers: readonly IExpressionParser[] = [absentValue, mockParser()];
+        const expectedError = 'missing leafs';
+        const parsers = absentCollection;
         // act
         const act = () => new CompositeExpressionParser(parsers);
         // assert
         expect(act).to.throw(expectedError);
-      });
+      }, { excludeUndefined: true, excludeNull: true });
     });
   });
   describe('findExpressions', () => {

tests/unit/application/Parser/Script/Compiler/Expressions/Parser/Regex/RegexParser.spec.ts

@@ -4,6 +4,7 @@ import { IPrimitiveExpression, RegexParser } from '@/application/Parser/Script/C
 import { ExpressionPosition } from '@/application/Parser/Script/Compiler/Expressions/Expression/ExpressionPosition';
 import { FunctionParameterStub } from '@tests/unit/shared/Stubs/FunctionParameterStub';
 import { itEachAbsentStringValue } from '@tests/unit/shared/TestCases/AbsentTests';
+import { expectExists } from '@tests/shared/Assertions/ExpectExists';
 
 describe('RegexParser', () => {
   describe('findExpressions', () => {
@@ -16,7 +17,7 @@ describe('RegexParser', () => {
         const act = () => sut.findExpressions(absentValue);
         // assert
         expect(act).to.throw(expectedError);
-      });
+      }, { excludeNull: true, excludeUndefined: true });
     });
     it('throws when position is invalid', () => {
       // arrange
@@ -30,17 +31,19 @@ describe('RegexParser', () => {
       ];
       const sut = new RegexParserConcrete(regexMatchingEmpty);
       // act
-      let error: string;
+      let errorMessage: string | undefined;
       try {
         sut.findExpressions(code);
       } catch (err) {
-        error = err.message;
+        errorMessage = err.message;
       }
       // assert
+      expectExists(errorMessage);
+      const error = errorMessage; // workaround for ts(18048): possibly 'undefined'
       expect(
         expectedErrorParts.every((part) => error.includes(part)),
         `Expected parts: ${expectedErrorParts.join(', ')}`
-          + `Actual error: ${error}`,
+          + `Actual error: ${errorMessage}`,
       );
     });
     describe('matches regex as expected', () => {
@@ -139,7 +142,7 @@ function mockBuilder(): (match: RegExpMatchArray) => IPrimitiveExpression {
   });
 }
 function getEvaluatorStub(): ExpressionEvaluator {
-  return () => undefined;
+  return () => `[${getEvaluatorStub.name}] evaluated code`;
 }
 
 function mockPrimitiveExpression(): IPrimitiveExpression {