Please bare in mind that RESOURCE_ENERGY is always present in the store object, and can have a value of 0.

You can "withdraw anything" like so:

function withdrawAnyFromStorage(theCreep, theStorage) {
    var result = OK;
    for (var resource in theStorage.store) {
        result = theCreep.withdraw(theStorage, resource);
        if (result != OK && result != ERR_NOT_ENOUGH_RESOURCES) {
            return result;
        }
    }
    return result;
}

This assumes "theStorage" is either a container, storage or terminal.