public V get(Object key) {
        if (key == null)
            return getForNullKey();
        int hash = 0;
        if (key instanceof String)
            hash = hash(hashString((String) key));
        else
            hash = hash(key.hashCode());
        for (Entry<K, V> e = table[indexFor(hash, table.length)]; e != null; e = e.next) {
            Object k;
            if (e.hash == hash && ((k = e.key) == key || key.equals(k)))
                return e.value;
        }
        return null;
    }
Returns the value to which the specified key is mapped, or {@code null}
if this map contains no mapping for the key.

<p>
More formally, if this map contains a mapping from a key {@code k} to a
value {@code v} such that {@code (key==null ? k==null :
key.equals(k))}, then this method returns {@code v}; otherwise it returns
{@code null}. (There can be at most one such mapping.)

<p>
A return value of {@code null} does not <i>necessarily</i> indicate that
the map contains no mapping for the key; it's also possible that the map
explicitly maps the key to {@code null}. The {@link #containsKey
containsKey} operation may be used to distinguish these two cases.

@see #put(Object, Object)
src/main/java/com/alibaba/fastjson/util/AntiCollisionHashMap.java