@SuppressWarnings("unchecked")
	@Nonnull
	public Collection<V> getIfPresent(K key) {
		return ((Map<K, Collection<V>>) backing).getOrDefault(key, Collections.emptyList());
	}
@param key
		Key to get a collection for.

@return A collection of values or an empty list, if none.
recaf-core/src/main/java/software/coley/recaf/util/MultiMap.java