public Object removeRealmPrincipal(String realmName, String principalName) {
        if (realmName == null) {
            throw new NullPointerException("realmName argument cannot be null.");
        }
        if (principalName == null) {
            throw new NullPointerException(("principalName argument cannot be null."));
        }
        if (this.realmPrincipals == null) {
            return null;
        }
        Map<String, Object> principals = this.realmPrincipals.get(realmName);
        if (principals != null) {
            return principals.remove(principalName);
        }
        return null;
    }
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