fix syntax

tween.cm

@@ -14,11 +14,12 @@ function make_engine(default_clock) {
       this.tweens = filter(this.tweens, t => t != tween)
     },
     update(current_time) {
-      if (current_time == null) {
-        current_time = this.default_clock ? this.default_clock() : time.number()
+      var ct = current_time
+      if (ct == null) {
+        ct = this.default_clock ? this.default_clock() : time.number()
       }
       arrfor(this.tweens, function(tween) {
-        tween._update(current_time)
+        tween._update(ct)
       })
     },
     clear() {
@@ -47,7 +48,7 @@ var TweenProto = {
       if (is_object(value)) {
         arrfor(array(value), subkey => {
           var flatKey = key + '.' + subkey
-          this.startVals[flatKey] = this.obj[key] ? this.obj[key][subkey] : undefined
+          this.startVals[flatKey] = this.obj[key] ? this.obj[key][subkey] : null
           this.endVals[flatKey] = value[subkey]
         })
       } else {
@@ -87,7 +88,7 @@ var TweenProto = {
 
   _update: function(now) {
     this.seek(now)
-    this.onUpdateCallback?.()
+    if (this.onUpdateCallback) this.onUpdateCallback()
   },
 
   seek: function(global_time) {
@@ -99,11 +100,14 @@ var TweenProto = {
       var start = this.startVals[key]
       var end = this.endVals[key]
       var value = start + (end - start) * eased
+      var parts = null
+      var objKey = null
+      var subKey = null
 
       if (search(key, '.') != null) {
-        var parts = array(key, '.')
-        var objKey = parts[0]
-        var subKey = parts[1]
+        parts = array(key, '.')
+        objKey = parts[0]
+        subKey = parts[1]
 
         if (!this.obj[objKey]) {
           this.obj[objKey] = {}