The AJP Connector is configured with secretRequired=”true” but the secret attribute is either null or “” after upgrade to 2.2.5

Navigate to the server.xml in tomcat:

Replace AJP with:

<Connector protocol="AJP/1.3" address="::1" port="8009"
           redirectPort="8443" secretRequired="false" />

But make sure that you understand the security implications of that (see Krzysztof Skrzynecki’s answer for that).