public static SerializerRegistration readClass(ByteBuffer buffer) {
        short classID = buffer.getShort();
        if (classID == -1) return NULL_CLASS;
        return idRegistrations.get(classID);
    }
Read the class from given buffer and return its SerializerRegistration.

@param buffer The buffer to read from.
@return The SerializerRegistration, or null if non-existent.
jme3-networking/src/main/java/com/jme3/network/serializing/Serializer.java