Java Wrapper /predict API regression

[amoldavsky]

Describe the bug

A regression in Seldon-Core 1.7.0 (and possibly many earlier versions) from 0.4.9 on the /predict API.
POST request with a proper JSON payload no longer working.

According to the docs here (and also the code):
https://docs.seldon.io/projects/seldon-core/en/latest/reference/upgrading.html#wrapper-compatibility-table

Only FORM data is supported, because a curl command without an explicit Content-Type header results in
application/x-www-form-urlencoded or multipart/form-data.

The JSON call from the docs does not work:

curl -s -X POST -H 'Content-Type: application/json' \
 -d '{"data": {"names": ["a", "b"], "ndarray": [[1.0, 2.0]]}}' \
 ${MODEL_URL}

To reproduce

This call used to work in 0.4.9 (and probably a few versions after)

curl -s -X POST \
	-H 'Content-Type: application/json' \
 	-d '{"jsonData":{ ... }}'
    $MODEL_URL

The above call no longer works and you get:

{"message":"Required String parameter 'json' is not present","error_code":400,"errors":[]}% 

Expected behaviour

Get a valid response like before for the following curl calls:

curl -s -X POST -H 'Content-Type: application/json' \
 -d '{"data": {"names": ["a", "b"], "ndarray": [[1.0, 2.0]]}}' \
 ${MODEL_URL}

curl -s -X POST -H 'Content-Type: application/json' \
 -d '{"jsonData": {"foo": "bar"}' \
 ${MODEL_URL}

Environment

Seldon-Core 1.7.0
Java Wrapper Jar 0.4.1
Java Wrapper image 0.2.0

Model Details

N/A

[amoldavsky]

discussion in the Slack channel:
https://seldondev.slack.com/archives/C8Y9A8G0Y/p1620740550073300