Is this a real concern? I don't think there's any way for a space to creep into a Java class-name? And, we should probably adjust `Strings.makeValidFilename` to remove spaces anyway. Then we _can_ just `return Strings.makeValidFilename(simpleName);` which I suggest we replace with this:

    public static String makeValidFilename(String s) {
        Preconditions.checkNotNull(s, "Cannot make valid filename from null string");
        return CharMatcher.anyOf(VALID_NON_ALPHANUM_FILE_CHARS).or(CharMatcher.JAVA_LETTER_OR_DIGIT)
                .negate()
                .collapseFrom(s, '_');
    }