test(http): add assertion for multipart placeholder logic when no files present

- Validates that '__multipart_placeholder__' is inserted to enforce multipart/form-data encoding.
- Ensures consistent behavior with backend servers expecting multipart format, even without file uploads.
- Adds condition to skip logging placeholder entries in logs to avoid noise.

api/core/workflow/nodes/http_request/executor.py

@@ -377,7 +377,10 @@ class Executor:
             raw += f"{k}: {v}\r\n"
 
         body_string = ""
-        if self.files:
+        # Only log actual files if present.
+        # '__multipart_placeholder__' is inserted to force multipart encoding but is not a real file.
+        # This prevents logging meaningless placeholder entries.
+        if self.files and not all(f[0] == "__multipart_placeholder__" for f in self.files):
             for key, (filename, content, mime_type) in self.files:
                 body_string += f"--{boundary}\r\n"
                 body_string += f'Content-Disposition: form-data; name="{key}"\r\n\r\n'

api/tests/unit_tests/core/workflow/nodes/http_request/test_http_request_executor.py

@@ -246,7 +246,9 @@ def test_executor_with_form_data():
     assert "multipart/form-data" in executor.headers["Content-Type"]
     assert executor.params == []
     assert executor.json is None
-    assert executor.files is None
+    # '__multipart_placeholder__' is expected when no file inputs exist,
+    # to ensure the request is treated as multipart/form-data by the backend.
+    assert executor.files == [('__multipart_placeholder__', ('', b'', 'application/octet-stream'))]
     assert executor.content is None
 
     # Check that the form data is correctly loaded in executor.data