fixup! fix: handle edge cases in namespacing

Author: AayushSabharwal

src/systems/abstractsystem.jl

@@ -1278,7 +1278,7 @@ function namespace_expr(
         end
     elseif isvariable(O)
         renamespace(n, O)
-    elseif O isa Array
+    elseif O isa AbstractArray
         let sys = sys, n = n
             map(o -> namespace_expr(o, sys, n; ivs), O)
         end