private void addBlock(BasicBlock block, IntList subroutines) {
    if (block == null) {
      throw new NullPointerException("block == null");
    }

    result.add(block);
    subroutines.throwIfMutable();
    resultSubroutines.add(subroutines);
  }
Adds a block to the output result.

@param block {@code non-null;} the block to add
@param subroutines {@code non-null;} subroutine label list as described in {@link
    Frame#getSubroutines}
android/android_framework/dex-maker/src/main/java/com/android/dx/cf/code/Ropper.java