REST notify forces "message" parameter in JSON

[tklenke]

The problem

homeassistant/components/rest/notify.py

If you send for example:
method: POST_JSON
data_template:
messages:
-source: "home assistant"
to: "+12345678"
body: "test msg"

you will get
{"message": "", "messages": [{"source": "homeassistant", "to": "+12345678", "body": "test msg"}]}

if you add:
message_param_name: ""

you will still get:
{"": "", "messages": [{"source": "homeassistant", "to": "+12345678", "body": "test msg"}]}

suggest adding check for length of message_param_name and if it is empty skip line 152
152: data = {self._message_param_name: message}
something like this maybe:
data = {self._message_param_name: message} if hasattr(message_param_name, 'len') and len(message_param_name) > 0 else {}

or maybe
data = {self._message_param_name: message} if message_param_name != "SUPPRESS_MESSAGE" else {}
probably is better...

What version of Home Assistant Core has the issue?

core

What was the last working version of Home Assistant Core?

No response

What type of installation are you running?

Home Assistant OS

Integration causing the issue

REST integration

Link to integration documentation on our website

No response

Diagnostics information

No response

Example YAML snippet

Anything in the logs that might be useful for us?

Additional information

No response