private void checkNotNull(final Object value, final String s) {
            if (value == null) {
                throw new IllegalArgumentException(s);
            }
        }
Validates the details of the SystemProperty, and generates one if it's valid.

@return A SystemProperty object
@throws IllegalArgumentException if incorrect arguments have been supplied to the builder
xmppserver/src/main/java/org/jivesoftware/util/SystemProperty.java