import java.util.concurrent.atomic.AtomicLong;
import javax.annotation.CheckForNull;

/**
 * A map containing {@code long} values that can be atomically updated. While writes to a
 * traditional {@code Map} rely on {@code put(K, V)}, the typical mechanism for writing to this map
 * is {@code addAndGet(K, long)}, which adds a {@code long} to the value currently associated with

     * that users *can* pass null arguments to Joiner, we annotate it as if it always tolerates null
     * inputs, rather than as if it never tolerates them.
     *
     * We rely on checkers to implement special cases to catch dangerous calls to join(), etc. based
     * on what they know about the particular Joiner instances the calls are performed on.
     *