public void setWhen(Predicate when) {
    this.when = when;
  }
Sets the expression (or {@link Predicate}) to use to determine when to include this Kerberos
identity while processing Kerberos identities.
<p>
<code>null</code> indicates there is nothing to evaluate and this Kerberos identity is to always
be included when processing Kerberos identities.

@param when a predicate
ambari-server/src/main/java/org/apache/ambari/server/state/kerberos/KerberosIdentityDescriptor.java