fix: input 컴포넌트 누락된 빈 값 핸들링 처리

src/components/survey-sale/detail/BasicForm.tsx

@@ -96,7 +96,7 @@ export default function BasicForm({ basicInfo, setBasicInfo, mode, session }: Ba
                       id="investigationDate"
                       type="date"
                       className="date-frame"
-                      value={basicInfo?.investigationDate?.toString()}
+                      value={basicInfo?.investigationDate?.toString() ?? ''}
                       onChange={(e) => setBasicInfo({ ...basicInfo, investigationDate: e.target.value })}
                     />
                   </div>