use === to compare with nothing

Author: s-broda

src/univariatearchmodel.jl

@@ -628,8 +628,8 @@ end
 function modname(::Type{S}) where S<:Union{UnivariateVolatilitySpec, MeanSpec}
     s = "$(S)"
 	lastcomma = findlast(isequal(','), s)
-	lastcomma == nothing || (s = s[1:lastcomma-1] * '}')
+	lastcomma === nothing || (s = s[1:lastcomma-1] * '}')
 	firstdot = findfirst(isequal('.'), s)
-	firstdot == nothing || (s = s[firstdot+1:end])
+	firstdot === nothing || (s = s[firstdot+1:end])
 	s
 end