�fix: prevent runtime error in josaPicker when word is empty string (#39

)

* fix: remove unnecessary not null assertions

* fix: 빈 문자열에 대한 런타임 오류 개선

* test: 엣지케이스에 대한 테스트 추가

src/josa.spec.ts

@@ -73,6 +73,9 @@ describe('Hangul', () => {
   });
 
   describe('josa.pick', () => {
+    it('첫 번째 매개변수가 빈 문자열이라면 옵션중 첫 번째 값을 반환한다', () => {
+      expect(josa.pick('', '이/가')).toBe('이');
+    });
     it('주격조사', () => {
       expect(josa.pick('샴푸', '이/가')).toBe('가');
       expect(josa.pick('칫솔', '이/가')).toBe('이');

src/josa.ts

@@ -29,10 +29,14 @@ export function josa(word: string, josa: JosaOption): string {
 josa.pick = josaPicker;
 
 function josaPicker(word: string, josa: JosaOption): string {
+  if (word.length === 0) {
+    return josa.split('/')[0];
+  }
+
   const has받침 = hasBatchim(word);
   let index = has받침 ? 0 : 1;
 
-  const is종성ㄹ = disassembleCompleteHangulCharacter(word[word.length - 1]!)?.last === 'ㄹ';
+  const is종성ㄹ = disassembleCompleteHangulCharacter(word[word.length - 1])?.last === 'ㄹ';
 
   const isCaseOf로 = has받침 && is종성ㄹ && 로_조사.includes(josa);
 
@@ -46,5 +50,5 @@ function josaPicker(word: string, josa: JosaOption): string {
     index = 1;
   }
 
-  return josa.split('/')[index]!;
+  return josa.split('/')[index];
 }