@SuppressWarnings("unchecked")
	public <C1 extends Collection<V>> MultiMapBuilder<K, V, C1> values(Supplier<C1> collectionSupplier) {
		this.collectionSupplier = (Supplier<Collection<V>>) collectionSupplier;
		return upgrade();
	}
@param collectionSupplier
		Collection supplier.
@param <C1>
		Backing collection type.

@return This builder.
recaf-core/src/main/java/software/coley/recaf/util/MultiMapBuilder.java