public void returnVoid() {
    if (!method.returnType.equals(TypeId.VOID)) {
      throw new IllegalArgumentException("declared " + method.returnType + " but returned void");
    }
    addInstruction(new PlainInsn(Rops.RETURN_VOID, sourcePosition, null, RegisterSpecList.EMPTY));
  }
Returns from a {@code void} method. After a return it is an error to define further
instructions after a return without first {@link #mark marking} an existing unmarked label.
android/android_framework/dex-maker/src/main/java/com/android/dx/Code.java