lib/modules: Fix freeform modules when there's no definitions

lib/modules.nix

@@ -104,7 +104,8 @@ rec {
                 file = def.file;
                 value = setAttrByPath def.prefix def.value;
               }) merged.unmatchedDefns;
-            in declaredConfig._module.freeformType.merge prefix defs;
+            in if defs == [] then {}
+            else declaredConfig._module.freeformType.merge prefix defs;
 
         in if declaredConfig._module.freeformType == null then declaredConfig
           # Because all definitions that had an associated option ended in

lib/tests/modules.sh

@@ -213,6 +213,8 @@ checkConfigError 'The option value .* in .* is not of type .*' \
 ## Freeform modules
 # Assigning without a declared option should work
 checkConfigOutput 24 config.value ./freeform-attrsOf.nix ./define-value-string.nix
+# No freeform assigments shouldn't make it error
+checkConfigOutput '{ }' config ./freeform-attrsOf.nix
 # but only if the type matches
 checkConfigError 'The option value .* in .* is not of type .*' config.value ./freeform-attrsOf.nix ./define-value-list.nix
 # and properties should be applied