How to add a space in a Concat expression

Good Morning!

Stupid question time......

I cannot seem to figure out the right syntax for this following concat statement.

${concat(entity.UserOptions.LocationSubType_c.DisplayLabel, ' ', entity.UserOptions.LocationNumber_c.DisplayLabel)}

What I am trying to do is to grab the results of two user selections and contat them into a string with a space between them.

UserOptionOne: TEST
UserOptionTwo: 999

Desired result: TEST 999

The problem is the space, the statement does not like the empty string.

So the question is, what syntax do I use to add the space between the two data statements?

Thank You,