Minor code review change.

frog/minfrog

Index: frog/minfrog
diff --git a/frog/minfrog b/frog/minfrog
index 6677f49bf511bce5e1398557bcbbc3e544abb3c5..a4f7d488047db53f0335d973562bacbc2543e5de 100755
--- a/frog/minfrog
+++ b/frog/minfrog
@@ -4899,9 +4899,7 @@ Parameter.prototype.resolve = function() {
   }
   this.type = this.method.resolveType(this.definition.type, false);
   if (this.definition.value != null) {
-    if (this.definition.value.span.start == this.definition.span.start) {
-      return;
-    }
+    if (!this.get$hasDefaultValue()) return;
     if (this.method.name == ":call") {
       if (this.method.get$definition().get$body() == null && !this.method.get$isNative()) {
         $globals.world.error("default value not allowed on function type", this.definition.span);
@@ -4936,6 +4934,9 @@ Parameter.prototype.copyWithNewType = function(newMethod, newType) {
 Parameter.prototype.get$isOptional = function() {
   return this.definition != null && this.definition.value != null;
 }
+Parameter.prototype.get$hasDefaultValue = function() {
+  return this.definition.value.span.start != this.definition.span.start;
+}
 Parameter.prototype.copyWithNewType$2 = Parameter.prototype.copyWithNewType;
 Parameter.prototype.genValue$2 = Parameter.prototype.genValue;
 Parameter.prototype.resolve$0 = Parameter.prototype.resolve;