返回结果为Null，然后应该怎么做。

[abbypop]

JNIEnv->FindClass(com/yxcorp/gifshow/util/CPU) was called from RX@0x1200240c[libcore.so]0x240c
JNIEnv->RegisterNatives(com/yxcorp/gifshow/util/CPU, RW@0x12006018[libcore.so]0x6018, 2) was called from RX@0x12002430[libcore.so]0x2430
RegisterNative(com/yxcorp/gifshow/util/CPU, getClock(Landroid/content/Context;[BI)Ljava/lang/String;, RX@0x12002030[libcore.so]0x2030)
RegisterNative(com/yxcorp/gifshow/util/CPU, getMagic(Landroid/content/Context;I)Ljava/lang/String;, RX@0x12002330[libcore.so]0x2330)
JNIEnv->GetMethodID(java/lang/Class.getName()Ljava/lang/String;) => 0x4a974877 was called from RX@0x12000aa0[libcore.so]0xaa0
JNIEnv->CallObjectMethodV(class android/content/Context, getName() => "android.content.Context") was called from RX@0x12000ba4[libcore.so]0xba4
JNIEnv->GetStringUtfChars("android.content.Context") was called from RX@0x12001868[libcore.so]0x1868
JNIEnv->ReleaseStringUTFChars("android.content.Context") was called from RX@0x12001894[libcore.so]0x1894
Exception in thread "main" java.lang.NullPointerException
at com.kuaishou.KuaishouSign.getSig(KuaishouSign.java:129)
at com.kuaishou.KuaishouSign.main(KuaishouSign.java:138)

设置参数的方法为：

public String getSig(String plainText) {
        List<Object> list = new ArrayList<>(10);
        list.add(vm.getJNIEnv());
        list.add(0);
        DvmObject<?> context = vm.resolveClass("android/content/Context").newObject(null);
        list.add(vm.addLocalObject(context));
        try {
            list.add(vm.addLocalObject(new ByteArray(vm, plainText.getBytes("UTF-8"))));
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        list.add(vm.addLocalObject(DvmInteger.valueOf(vm, 23)));
        Number number = module.callFunction(emulator,0x2030, list.toArray());
        String result = vm.getObject(number.intValue()).getValue().toString();
        return result;
}