JsonPath in Key for Set Variable not resolving

[josephjacobmorris]

Task Definition

{
  "name": "update_task_migrate_0",
  "taskReferenceName": "update_task_migrate_0",
  "inputParameters": {
    "${task_migrate_0.output.refId}": "${task_migrate_0.output}"
  },
  "type": "SET_VARIABLE",
  "startDelay": 0,
  "optional": false,
  "asyncComplete": false
}

During execution the key is not getting resolved while the value is getting resolved

{
  "${task_migrate_0.output.refId}": {
    "subWorkflowId": "cab266f5-43b1-450e-a59b-5f35ca696bcd",
    "taskId": "bc4468fd-f168-4842-9bde-8a681d1a2aac",
    "refId": "buylistproduct#935"
  }
}

Can you help me understand what is the issue ?
I tried going thru the code and found that in ParameterUtils , we are only replacing the values and not the keys as shown in below snippet.

private Map<String, Object> replace(
            Map<String, Object> input, DocumentContext documentContext, String taskId) {
        Map<String, Object> result = new HashMap<>();
        for (Entry<String, Object> e : input.entrySet()) {
            Object newValue;
            Object value = e.getValue();
            if (value instanceof String) {
                newValue = replaceVariables(value.toString(), documentContext, taskId);
            } else if (value instanceof Map) {
                // recursive call
                newValue = replace((Map<String, Object>) value, documentContext, taskId);
            } else if (value instanceof List) {
                newValue = replaceList((List<?>) value, taskId, documentContext);
            } else {
                newValue = value;
            }
            result.put(e.getKey(), newValue);
        }
        return result;
    }

Is this being done due to some reason which I am not aware of?
Alternative approaches would also be appreciated .