public Set asSet() {
        if (CollectionUtils.isEmpty(this.combinedPrincipals)) {
            return Collections.emptySet();
        }
        Set<Object> set = new HashSet<Object>(this.combinedPrincipals.size());
        set.addAll(this.combinedPrincipals.values());
        return set;
    }
Default implementation of the {@link PrincipalMap} interface.
<p>
*EXPERIMENTAL for Shiro 1.2 - DO NOT USE YET*

@since 1.2
core/src/main/java/org/apache/shiro/subject/SimplePrincipalMap.java