deal with corner case.

src/builtins/builtins-encoder.cc

@@ -141,7 +141,6 @@ BUILTIN(Close) {
         return *isolate->factory()->ToBoolean(true);
     }
 
-    std::remove(enc->getOutputPath().c_str());
     enc->close();
     enc = nullptr;
     inited = false;
@@ -225,6 +224,12 @@ BUILTIN(Save) {
 BUILTIN(AddAudioBuffer) {
     HandleScope scope(isolate);
 
+
+    Handle<Object> audioBuffer = args.atOrUndefined(isolate, 1);
+    if (audioBuffer->IsUndefined() || audioBuffer->IsNull()) {
+        return ReadOnlyRoots(isolate).undefined_value();
+    }
+
     Handle<JSTypedArray> array;
     ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, array,
         JSTypedArray::Validate(isolate, args.atOrUndefined(isolate, 1), "ENCODER.encode()"));
@@ -252,7 +257,13 @@ BUILTIN(AddAudioBuffer) {
 BUILTIN(MergeMP4) {
     HandleScope scope(isolate);
 
+    if (!audioPath) {
+        return *(isolate->factory()->
+                 NewStringFromAsciiChecked(enc->getOutputPath().c_str()));
+    }
+
     Handle<Object> libpath = args.atOrUndefined(isolate, 1);
+
     // Libav path
     std::string libpath_cppstr;
     if (libpath->IsUndefined()) {
@@ -284,6 +295,7 @@ BUILTIN(MergeMP4) {
 
     free(audioPath);
     audioPath = nullptr;
+    std::remove(enc->getOutputPath().c_str());
 
     return *mergepath;
 }