title: Cas calling /proxy to get proxy ticket return NPE
body: <p>I am trying to get proxy ticket after received pgtiou and pgtid</p>
  <p>Following are detai:</p>
  <p>cas version: 5.0.10
  api to get proxy ticket: https://localhost:8443/cas/proxy?pgt=PGT-123&amp;targetService=https://localhost:8085/proxycallback
  500 status code received. on the log:</p>
  <pre><code>java.lang.NullPointerException
  at org.apereo.cas.web.ProxyController.getTargetService(ProxyController.java:102) ~[cas-server-support-validation-5.0.10.jar:5.0.10]
  at org.apereo.cas.web.ProxyController.handleRequestInternal(ProxyController.java:78) ~[cas-server-support-validation-5.0.10.jar:5.0.10]
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_281]
  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_281]
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_281]
  at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_281]
  </code></pre>
  <p>config on service registry:</p>
  <pre><code>{
    &quot;@class&quot; : &quot;org.apereo.cas.services.RegexRegisteredService&quot;,
    &quot;serviceId&quot; : &quot;^(https?|imaps?)://.*&quot;,
    &quot;name&quot; : &quot;HTTPS and IMAPS&quot;,
    &quot;id&quot; : 10000001,
    &quot;description&quot; : &quot;This service definition authorizes all application urls that support HTTPS and IMAPS protocols.&quot;,
    &quot;evaluationOrder&quot; : 10000,
    &quot;attributeReleasePolicy&quot; : {
      &quot;@class&quot; : &quot;org.apereo.cas.services.ReturnAllowedAttributeReleasePolicy&quot;,
      &quot;principalAttributesRepository&quot; : {
        &quot;@class&quot; : &quot;org.apereo.cas.authentication.principal.DefaultPrincipalAttributesRepository&quot;
      },
      &quot;authorizedToReleaseCredentialPassword&quot; : false,
      &quot;authorizedToReleaseProxyGrantingTicket&quot; : true
    },
     &quot;proxyPolicy&quot; : {
      &quot;@class&quot; : &quot;org.apereo.cas.services.RegexMatchingRegisteredServiceProxyPolicy&quot;,
      &quot;pattern&quot; : &quot;^https?://.*&quot;
    }
    ,
     &quot;publicKey&quot; : {
      &quot;@class&quot; : &quot;org.apereo.cas.services.RegisteredServicePublicKeyImpl&quot;,
      &quot;location&quot; : &quot;classpath:public.key&quot;,
      &quot;algorithm&quot; : &quot;RSA&quot;
    }
  }
  </code></pre>