Adding a key with an empty value to Guava Multimap

I have a need to add a key to a Guava Multimap with an empty collection as the value. How do I accomplish this?

I tried this:

map.put( "my key", null );

but calling get() returns a list with one element, which is null. I worked around this by doing the following:

map.putAll("my key2", new ArrayList())

but I'm wondering if this is a bad thing to do? I know Guava automatically removes a key when the last value is removed to keep containsKey() consistent. What's my best option here?