Merge "Fix NDEF documentation to indicate the message may be null."

    boolean isPresent(int nativeHandle);

    TransceiveResult transceive(int nativeHandle, in byte[] data, boolean raw);

    int getLastError(int nativeHandle);

    NdefMessage ndefRead(int nativeHandle);

    int ndefWrite(int nativeHandle, in NdefMessage msg);

    int ndefMakeReadOnly(int nativeHandle);

     * <p>If the NDEF Message is modified by an I/O operation then it

     * will not be updated here, this function only returns what was discovered

     * when the tag entered the field.

     * <p>Note that this method may return null if the tag was in the

     * INITIALIZED state as defined by NFC Forum, as in this state the

     * tag is formatted to support NDEF but does not contain a message yet.

     * <p>Does not cause any RF activity and does not block.

     * @return NDEF Message read from the tag at discovery time

     * @return NDEF Message read from the tag at discovery time, can be null

     */

    public NdefMessage getCachedNdefMessage() {

        return mNdefMsg;

     *

     * <p>This always reads the current NDEF Message stored on the tag.

     *

     * <p>Note that this method may return null if the tag was in the

     * INITIALIZED state as defined by NFC Forum, as in that state the

     * tag is formatted to support NDEF but does not contain a message yet.

     *

     * <p>This is an I/O operation and will block until complete. It must

     * not be called from the main application thread. A blocked call will be canceled with

     * {@link IOException} if {@link #close} is called from another thread.

     *

     * @return the NDEF Message, never null

     * @return the NDEF Message, can be null

     * @throws TagLostException if the tag leaves the field

     * @throws IOException if there is an I/O failure, or the operation is canceled

     * @throws FormatException if the NDEF Message on the tag is malformed

            int serviceHandle = mTag.getServiceHandle();

            if (tagService.isNdef(serviceHandle)) {

                NdefMessage msg = tagService.ndefRead(serviceHandle);

                if (msg == null) {

                    int errorCode = tagService.getLastError(serviceHandle);

                    switch (errorCode) {

                        case ErrorCodes.ERROR_IO:

                            throw new IOException();

                        case ErrorCodes.ERROR_INVALID_PARAM:

                            throw new FormatException();

                        default:

                            // Should not happen

                            throw new IOException();

                    }

                if (msg == null && !tagService.isPresent(serviceHandle)) {

                    throw new TagLostException();

                }

                return msg;

            } else {