labeling in Arcade

[IngridAnneessens]

I want to label my feature as follows:

when ADRESSTATUS = Gehistoreeerd -> No label
when BUSNUMMER = Null --> Huinummer
When BUSNUMMER is not NULL --> Huisnumer underlined

I keep getting an 'invalid expression' 
Can anyone see what's wrong here? Is there a beter way tot do this?

[ChristopherCounsell]

You are missing a ')' at the end of line 5.

[IngridAnneessens]

I don't see where I have to put it:
if (!IsEmpty(Busnummer)) {return + Huisnummer};

[JohannesLindner · Accepted solution]

tl;dr:

return When(
    Adresstatus == "Gehistoreerd", null,
    IsEmpty(Busnummer), Huisnummer,
    !IsEmpty(Busnummer), `<UND>${Huisnummer}</UND>`,
    "Default value"
    )

A few pointers:

• return + something is not valid syntax. return something is. More info on return.
• = is for assignment (this variable now has this value), == is for comparison (does this variable have this value?) More info on operators.
• You can append multiple string values (what you tried with the <u>), but you have to actually make them strings using quotation marks, and you have to either add them ("<UND>" + Huisnummer + "</UND>") or use template literals, which I did above.
• Label formatting tags are not the same as HTML tags.
• For chained if-then blocks, you can use the When function.

[IngridAnneessens]

Thank you, Johannes!