superagent: fix field() multipart generation

src/superagent.js

@@ -185,11 +185,7 @@ class Request {
 
         const partHeader = Buffer.from(`--${this.#boundary}\r\nContent-Disposition: form-data; name="${name}"\r\n\r\n`, 'utf8');
         const partData = Buffer.from(value, 'utf8');
-        const partTrailer = Buffer.from(`\r\n--${this.#boundary}--\r\n`, 'utf8');
-        this.#body = Buffer.concat([this.#body, partHeader, partData, partTrailer]);
-
-        this.#options.headers['content-type'] = `multipart/form-data; boundary=${this.#boundary}`;
-        this.#options.headers['content-length'] = this.#body.byteLength;
+        this.#body = Buffer.concat([this.#body, partHeader, partData, Buffer.from('\r\n', 'utf8')]);
 
         return this;
     }
@@ -199,16 +195,20 @@ class Request {
 
         const partHeader = Buffer.from(`--${this.#boundary}\r\nContent-Disposition: form-data; name="${name}" filename="${path.basename(filepath)}"\r\n\r\n`, 'utf8');
         const partData = fs.readFileSync(filepath);
-        const partTrailer = Buffer.from(`\r\n--${this.#boundary}--\r\n`, 'utf8');
-        this.#body = Buffer.concat([this.#body, partHeader, partData, partTrailer]);
-
-        this.#options.headers['content-type'] = `multipart/form-data; boundary=${this.#boundary}`;
-        this.#options.headers['content-length'] = this.#body.byteLength;
+        this.#body = Buffer.concat([this.#body, partHeader, partData, Buffer.from('\r\n', 'utf8')]);
 
         return this;
     }
 
     then(onFulfilled, onRejected) {
+        if (this.#boundary) {
+            const partTrailer = Buffer.from(`--${this.#boundary}--\r\n`, 'utf8');
+            this.#body = Buffer.concat([this.#body, partTrailer]);
+
+            this.#options.headers['content-type'] = `multipart/form-data; boundary=${this.#boundary}`;
+            this.#options.headers['content-length'] = this.#body.byteLength;
+        }
+
         this._start().then(onFulfilled, onRejected);
     }
 }