private static boolean isEmpty(Collection c) {
        return c == null || c.isEmpty();
    }
Assert a boolean expression, throwing {@link IllegalStateException}
if the test result is <code>false</code>.
<p>Call {@link #isTrue(boolean)} if you wish to
throw {@link IllegalArgumentException} on an assertion failure.
<pre class="code">Assert.state(id == null);</pre>

@param expression a boolean expression
@throws IllegalStateException if the supplied expression is <code>false</code>
lang/src/main/java/org/apache/shiro/lang/util/Assert.java