If statement in new node expresion

Hi all

I am sorry if this sounds very basic question. please note i don’t have coding background hence often find difficulty in writing even the simplest code.

I have 10 fields where the entries are as follows:

L9_layer contains either “B9” or “No B9”

L7_layer contains either “B7” or “No B7”

L2_layer contains either “B2” or “No B2”

L3_layer contains either “B3” or “No B3”

L23_layer contains either “B23” or “No B23”

n7_layer contains either “n7” or “No n7”

n23_layer contains either “n23” or “No n23”

n70_layer contains either “n70” or “No n70”

in the new field called layerconfig, i want blank if all the layers has no entries meaning all the layers have “Noxxx” corresponding values but if any of these have other than “No_xxx” i want to combine them. Like if L9 and L7 has B9 & B7, it should return B9/B7 and if B9 has “No B9”, then it should be “B7”

this means it will combine all the values together separated by “/” if the values are other than “No” in it.

i was trying the following expression

if(

$[“L9_layer”] = "No B9,

if($[“L7layer”] = “No B7”, “”, $[“L7layer”]),

if($[“L7layer”] = “No B28”, $[“L9layer”], join($[“L9layer”], “/”, $[“L700layer”]))

)

but the value o am getting is “/B7B9” instead of B7/B9

Can any one help what wrong i am doing?

thank you very much in advance