public void add(NameValuePair pair) {
    throwIfImmutable();

    if (pair == null) {
      throw new NullPointerException("pair == null");
    }

    CstString name = pair.getName();

    if (elements.get(name) != null) {
      throw new IllegalArgumentException("name already added: " + name);
    }

    elements.put(name, pair);
  }
Add an element to the set of (name, value) pairs for this instance. It is an error to call this
method if there is a preexisting element with the same name.

@param pair {@code non-null;} the (name, value) pair to add to this instance
android/android_framework/dex-maker/src/main/java/com/android/dx/rop/annotation/Annotation.java