Replace @Nonnull annotation with requireNonNull assertion

Change-Id: Icdef91e75b51e5836cd5c141d88c13dc83945f4c
diff --git a/src/main/java/com/thesamet/gerrit/plugins/saml/SamlWebFilter.java b/src/main/java/com/thesamet/gerrit/plugins/saml/SamlWebFilter.java
index 66313d2..1550703 100644
--- a/src/main/java/com/thesamet/gerrit/plugins/saml/SamlWebFilter.java
+++ b/src/main/java/com/thesamet/gerrit/plugins/saml/SamlWebFilter.java
@@ -24,7 +24,7 @@
 import java.util.Enumeration;
 import java.util.HashSet;
 import java.util.List;
-import javax.annotation.Nonnull;
+import java.util.Objects;
 import javax.servlet.Filter;
 import javax.servlet.FilterChain;
 import javax.servlet.FilterConfig;
@@ -238,9 +238,9 @@
   private class AuthenticatedHttpRequest extends HttpServletRequestWrapper {
     private AuthenticatedUser user;
 
-    public AuthenticatedHttpRequest(HttpServletRequest request, @Nonnull AuthenticatedUser user) {
+    public AuthenticatedHttpRequest(HttpServletRequest request, AuthenticatedUser user) {
       super(request);
-      this.user = user;
+      this.user = Objects.requireNonNull(user, "user");
     }
 
     @Override