Elytron SASL factories don't follow contract from corresponding Java interfaces

Java SaslClientFactory and SaslServerFactory interfaces define where null parameters or null return values are allowed and which Exception types can be used in methods. Elytron implementation of SASL mechanisms doesn't follow this contract, which results in NullPointerExceptions.

E.g.

java.lang.NullPointerException
	at org.wildfly.security.sasl.scram.ScramSaslClientFactory.getMechanismNames(ScramSaslClientFactory.java:119)
...