docs: @CheckForNull
      static public BitSet getBytecodeSet(JavaClass clazz, Method method) {
  
          XMethod xmethod = XFactory.createXMethod(clazz, method);
          if (cachedBitsets().containsKey(xmethod)) {
              return cachedBitsets().get(xmethod);
          }
          Code code = method.getCode();
          if (code == null) {
              return null;
          }
  
          byte[] instructionList = code.getCode();
  
          // Create callback
          UnpackedBytecodeCallback callback = new UnpackedBytecodeCallback(instructionList.length);
  
          // Scan the method.
          BytecodeScanner scanner = new BytecodeScanner();
          scanner.scan(instructionList, callback);
  
          UnpackedCode unpackedCode = callback.getUnpackedCode();
          BitSet result = null;
          if (unpackedCode != null) {
              result = unpackedCode.getBytecodeSet();
          }
          cachedBitsets().put(xmethod, result);
          return result;
      }