[NF] Handle empty arrays better.

Belonging to [master]:
  - #2183
  - OpenModelica/OpenModelica-testsuite#849

Author: perost

Compiler/NFFrontEnd/NFExpression.mo

@@ -2069,8 +2069,14 @@ public
       case CREF(cref = ComponentRef.CREF())
         algorithm
           subs := expandCref2(crefExp.cref);
+
+          if listEmpty(subs) then
+            arrayExp := ARRAY(Type.ARRAY(Type.arrayElementType(crefExp.ty), {Dimension.INTEGER(0)}), {});
+          else
+            arrayExp := expandCref3(subs, crefExp.cref, Type.arrayElementType(crefExp.ty));
+          end if;
         then
-          expandCref3(subs, crefExp.cref, Type.arrayElementType(crefExp.ty));
+          arrayExp;
 
       else crefExp;
     end match;
@@ -2091,7 +2097,7 @@ public
           dims := Type.arrayDims(cref.ty);
           cr_subs := Subscript.expandList(cref.subscripts, dims);
         then
-          expandCref2(cref.restCref, cr_subs :: subs);
+          if listEmpty(cr_subs) then {} else expandCref2(cref.restCref, cr_subs :: subs);
 
       else subs;
     end match;

Compiler/NFFrontEnd/NFScalarize.mo

@@ -102,6 +102,11 @@ algorithm
   if Type.isArray(var.ty) then
     Variable.VARIABLE(name, ty, binding, vis, attr, ty_attr, cmt, info) := var;
     crefs := ComponentRef.scalarize(name);
+
+    if listEmpty(crefs) then
+      return;
+    end if;
+
     ty := Type.arrayElementType(ty);
     (ty_attr_names, ty_attr_iters) := scalarizeTypeAttributes(ty_attr);
 

Compiler/NFFrontEnd/NFSubscript.mo

@@ -303,14 +303,29 @@ public
   protected
     Dimension dim;
     list<Dimension> rest_dims = dimensions;
+    list<Subscript> subs;
   algorithm
     for s in subscripts loop
       dim :: rest_dims := rest_dims;
-      outSubscripts := expand(s, dim) :: outSubscripts;
+      subs := expand(s, dim);
+
+      if listEmpty(subs) then
+        outSubscripts := {};
+        return;
+      else
+        outSubscripts := subs :: outSubscripts;
+      end if;
     end for;
 
     for d in rest_dims loop
-      outSubscripts := RangeIterator.map(RangeIterator.fromDim(d), makeIndex) :: outSubscripts;
+      subs := RangeIterator.map(RangeIterator.fromDim(d), makeIndex);
+
+      if listEmpty(subs) then
+        outSubscripts := {};
+        return;
+      else
+        outSubscripts := subs :: outSubscripts;
+      end if;
     end for;
 
     outSubscripts := listReverse(outSubscripts);

Compiler/Util/List.mo

@@ -6935,8 +6935,12 @@ public function combination<TI>
 protected
   list<list<TI>> elems;
 algorithm
-  elems := combination_tail(inElements, {}, {});
-  outElements := listReverse(elems);
+  if listEmpty(inElements) then
+    outElements := {};
+  else
+    elems := combination_tail(inElements, {}, {});
+    outElements := listReverse(elems);
+  end if;
 end combination;
 
 protected function combination_tail<TI>