arcgis desktop - If-Then Label Expression

I'm trying to create a VB label expression on streets such that streets with an alternate name (ACS_ALIAS) will be labeled with the LABEL name and the alternate name in parentheses; streets with no alternate name will be labeled with the LABEL name only. Here is what I tried but to no avail:

Function FindLabel ( [LABEL], [ACS_ALIAS] )

if ( [ACS_ALIAS] <>  ) then

FindLabel = ( [LABEL] & " (" & [ACS_ALIAS] & ")" )

elseif ( [ACS_ALIAS] =  ) then


FindLabel = [LABEL]

end if

End Function

I can only think of some non-expression workarounds.