fix: appropriately map array variables to scalarized versions in add_fallbacks!

Author: AayushSabharwal

src/systems/problem_utils.jl

@@ -117,6 +117,7 @@ Variables as they are specified in `vars` will take priority over their `toterm`
 function add_fallbacks!(
         varmap::AnyDict, vars::Vector, fallbacks::Dict; toterm = default_toterm)
     missingvars = Set()
+    arrvars = Set()
     for var in vars
         haskey(varmap, var) && continue
         ttvar = toterm(var)
@@ -158,6 +159,7 @@ function add_fallbacks!(
                 if val !== nothing
                     val = val[idxs...]
                 end
+                push!(arrvars, arrvar)
             else
                 val = nothing
             end
@@ -170,6 +172,10 @@ function add_fallbacks!(
         end
     end
 
+    for arrvar in arrvars
+        varmap[arrvar] = collect(arrvar)
+    end
+
     return missingvars
 end