HTTP Post with files works with Requests but not HTTPX #481

import requests
import uuid
import subprocess
import json
import os
import httpx

newName = uuid.uuid4().hex
event = uuid.uuid4().hex

subprocess.call("cp index.jpeg /tmp/%s.jpeg"%(newName),shell=True)

url = 'http://myserver.us-west-2.compute.amazonaws.com'

event = "ASDGASFDASDF"
payload = {'event': "%s"%(event) , 'confidence': 95}

thermalName = "/tmp/%s.jpeg"%(newName)
newName = thermalName

files = {

        'json': (None, json.dumps(payload), 'application/json'),
        'image': (os.path.basename(newName), open(newName, 'rb'), 'application/octet-stream'),
        'image1': (os.path.basename(newName), open(newName, 'rb'), 'application/octet-stream'),
        'image2': (os.path.basename(newName), open(newName, 'rb'), 'application/octet-stream')

        }

# Do the HTTP POST
#r = requests.post(url, files=files)
r = httpx.post(url, files=files)
print(r.text)

Traceback (most recent call last):
  File "test-post.py", line 32, in <module>
    r = httpx.post(url, files=files)
  File "/usr/local/lib/python3.6/dist-packages/httpx/api.py", line 183, in post
    trust_env=trust_env,
  File "/usr/local/lib/python3.6/dist-packages/httpx/api.py", line 53, in request
    trust_env=trust_env,
  File "/usr/local/lib/python3.6/dist-packages/httpx/client.py", line 718, in request
    cookies=cookies,
  File "/usr/local/lib/python3.6/dist-packages/httpx/client.py", line 336, in build_request
    cookies=cookies,
  File "/usr/local/lib/python3.6/dist-packages/httpx/models.py", line 696, in __init__
    content, content_type = self.encode_data(data, files, json)
  File "/usr/local/lib/python3.6/dist-packages/httpx/models.py", line 619, in encode_data
    content, content_type = multipart_encode(data or {}, files)
  File "/usr/local/lib/python3.6/dist-packages/httpx/multipart.py", line 103, in multipart_encode
    body.write(field.render_headers())
  File "/usr/local/lib/python3.6/dist-packages/httpx/multipart.py", line 66, in render_headers
    filename = _format_param("filename", self.filename)
  File "/usr/local/lib/python3.6/dist-packages/httpx/multipart.py", line 121, in _format_param
    value = _HTML5_FORM_ENCODING_RE.sub(replacer, value)
TypeError: expected string or bytes-like object