Empty subflow property used in config for node in subflow replaced with ${<name>} instead of empty string

[colinl]

Current Behavior

If a subflow property is left empty and is used in a contained node config as ${name} then that is replaced with the text ${name} instead of an empty string.
I am using it to pass a class to a contained dashboard 2 node and the result is that it ends up with a class of ${class}.

Expected Behavior

It should be an empty string, I think.

Steps To Reproduce

Import the flow below and run it.

Example flow

[{"id":"0a1d6e22b709848d","type":"subflow","name":"Empty property test","info":"","category":"","in":[],"out":[{"x":400,"y":80,"wires":[{"id":"48fce04ebb8a6bbe","port":0}]},{"x":400,"y":180,"wires":[{"id":"14b4297f97abdf9c","port":0}]}],"env":[{"name":"value1","type":"str","value":""},{"name":"value2","type":"str","value":""}],"meta":{},"color":"#DDAA99"},{"id":"48fce04ebb8a6bbe","type":"inject","z":"0a1d6e22b709848d","name":"","props":[{"p":"payload"}],"repeat":"5","crontab":"","once":true,"onceDelay":0.1,"topic":"","payload":"${value1}","payloadType":"str","x":210,"y":80,"wires":[[]]},{"id":"14b4297f97abdf9c","type":"inject","z":"0a1d6e22b709848d","name":"","props":[{"p":"payload"}],"repeat":"5","crontab":"","once":true,"onceDelay":0.1,"topic":"","payload":"${value2}","payloadType":"str","x":210,"y":180,"wires":[[]]},{"id":"ad46caabb2f31ef4","type":"debug","z":"33d99109.14b49e","name":"VALUE 1","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":640,"y":400,"wires":[]},{"id":"9dc2dc5cebac6292","type":"debug","z":"33d99109.14b49e","name":"VALUE 2","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":640,"y":460,"wires":[]},{"id":"cafd616b39449568","type":"subflow:0a1d6e22b709848d","z":"33d99109.14b49e","name":"empty property test","env":[{"name":"value2","value":"v2","type":"str"}],"x":350,"y":440,"wires":[["ad46caabb2f31ef4"],["9dc2dc5cebac6292"]]}]

Environment

• Node-RED version: 3.1.9 and 4.0.0-Beta.2
• Node.js version: 16 and 20
• npm version:
• Platform/OS:Ubuntu on laptop and Pi OS on Pi
• Browser: Edge

[knolleary]

This is how we've always handled env-var substitution into node properties if the env var is blank. It isn't specific to subflows, or the config node option.

If you change the typedInput to env type, then it will evaluate to an empty string:

[colinl]

In D2 ui-template the class field is not a typed input, so I can't do that.

There is a workaround, by adding a node in front of the template that sets message.class from the env var instead.

[knolleary]

I've opened #4672 for 4.0 that will allow blank strings to be inserted via env vars. Undefined env vars will still leave the ${FOO} value untouched.

[colinl]

Thanks.
For the record, for typed inputs, setting it as Env Var type works, though the syntax is