에러 the request doesn't contain a multipart/form-data or multipart/mixed stream

Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.web.multipart.MultipartException: Failed to parse multipart servlet request; nested exception is javax.servlet.ServletException: org.apache.tomcat.util.http.fileupload.impl.InvalidContentTypeException: the request doesn't contain a multipart/form-data or multipart/mixed stream, content type header is application/json] with root cause
org.apache.tomcat.util.http.fileupload.impl.InvalidContentTypeException: the request doesn't contain a multipart/form-data or multipart/mixed stream, content type header is application/json

## 해결책 1 

try {
        const response = await fetch('/api/reportMail', {
            method: 'POST',
            body: sendData,  // Content-Type을 설정하지 않음
        });

        if (!response.ok) {
            throw new Error('Something went wrong');
        }

        const result = await response.json();
        console.log('Server response:', result);

    } catch (error) {
        console.error('Error:', error);
    }
    
    전송시에 content-type을 따로 명시하지않음

결과 Completed 415 UNSUPPORTED_MEDIA_TYPE -→ 오타로인한것임