public static void setFinal(FieldNode field, boolean isFinal) {
    int modifiers = field.getModifiers();
    if (isFinal) {
      modifiers |= Opcodes.ACC_FINAL;
    } else {
      modifiers &= ~(Opcodes.ACC_FINAL);
    }
    field.setModifiers(modifiers);
  }
Turns an argument list obtained from AstUtil.getArguments() into an Object[] array
suitable to be passed to InvokerHelper or SpockRuntime. The main challenge is
to handle SpreadExpression's correctly.
spock-core/src/main/java/org/spockframework/compiler/AstUtil.java