In case when implementation of asString(StringBuilder b) for MatchRule does not change length of passed parameter (which is 0) then 'java.lang.StringIndexOutOfBoundsException: String index out of range: -1' is thrown for calling MatchRule.toString() due to calling StringBuilder.setLength(-1).

e.g. MatchRule ALL in implementation asString(StringBuilder b) just returns passed parameter, which results to mentioned exception.

Thrown exception:

java.lang.StringIndexOutOfBoundsException: String index out of range: -1
	at java.lang.AbstractStringBuilder.setLength(AbstractStringBuilder.java:180)
	at java.lang.StringBuilder.setLength(StringBuilder.java:76)
	at org.wildfly.security.auth.client.MatchRule.toString(MatchRule.java:581)
    ...