@Nullable
    private Boolean getActiveFilterSavedDifferently() {
        if (currentCacheFilter.get().isFiltering()) {
            return currentCacheFilter.get().isSavedDifferently();
        }
        return null;
    }
Check if a given username is valid (non blank), and show a toast if it isn't.

@param context  an activity
@param username the username to check
@return <tt>true</tt> if the username is not blank, <tt>false</tt> otherwise
main/src/main/java/cgeo/geocaching/CacheListActivity.java