Error message for ValueError: boundary missed for Content-Type: multipart/form-data

Error handling request
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/site-packages/aiohttp/web_protocol.py", line 418, in start
    resp = await task
  File "/usr/local/lib/python3.8/site-packages/aiohttp/web_app.py", line 458, in _handle
    resp = await handler(request)
  File "/document_service/prozorro_sale/document_service/api.py", line 35, in upload_document
    data = await request.multipart()
  File "/usr/local/lib/python3.8/site-packages/aiohttp/web_request.py", line 588, in multipart
    return MultipartReader(self._headers, self._payload)
  File "/usr/local/lib/python3.8/site-packages/aiohttp/multipart.py", line 530, in __init__
    self._boundary = ('--' + self._get_boundary()).encode()
  File "/usr/local/lib/python3.8/site-packages/aiohttp/multipart.py", line 627, in _get_boundary
    raise ValueError('boundary missed for Content-Type: %s'
ValueError: boundary missed for Content-Type: multipart/form-data