In 5.0.1 the generated line in `ApiClient` was:
```
return RequestBody.create(MediaType.parse(contentType), (byte[]) obj);
```
in 5.1.0 it is:
```
return RequestBody.create((byte[]) obj, MediaType.parse(contentType));
```
Looks like this change was introduced in #8969, and requires a more recent version of OkHttp to compile in some (all?) circumstances.
83adc064a4