public Integer remove(Object key) {
        IntegerFieldValue ifv = map.remove(key);
        return ifv != null ? ifv.getInteger() : null;
    }
Remove a key-weight association from this set.

@param key the key to remove
@return the weight that was previously associated with this key, or null (if there was no previous key)
document/src/main/java/com/yahoo/document/datatypes/WeightedSet.java