StringUtils.equals(cs1,cs2) delegates to CharSequence.regionMatches(...) in a way that causes IndexOutOfBounds when either of cs1/cs2 isn't a String.
Specifically, comparing "foo" and "foobar" for non-String CharSequences bombs due to CharSequenceUtils.regionMatches(cs1, false, 0, cs2, 0, Math.max(cs1.length(), cs2.length())) because regionMatches doesn't check for input exhaustion. Bug appears in default. - Aman
