Use invokeStatic instead of Functions

core/src/main/java/hudson/Functions.java

@@ -2285,18 +2285,4 @@ public static boolean isContextMenuVisible(Action a) {
             return true;
         }
     }
-
-    @Restricted(NoExternalUse.class)
-    @CheckForNull
-    public static Header header() {
-        List<Header> headers = ExtensionList.lookup(Header.class).stream().filter(header -> header.isHeaderEnabled()).collect(Collectors.toList());
-        if (headers.size() > 0) {
-            if (headers.size() > 1) {
-                LOGGER.warning("More than one configured header. This should not happen. Serving the Jenkins default header and please review");
-            } else {
-                return headers.get(0);
-            }
-        }
-        return new JenkinsHeader();
-    }
 }

core/src/main/java/jenkins/views/JenkinsHeader.java

@@ -1,13 +1,38 @@
 package jenkins.views;
 
+import java.util.List;
+import java.util.logging.Logger;
+import java.util.stream.Collectors;
+
+import org.kohsuke.accmod.Restricted;
+import org.kohsuke.accmod.restrictions.NoExternalUse;
+
+import edu.umd.cs.findbugs.annotations.CheckForNull;
 import hudson.Extension;
+import hudson.ExtensionList;
 
 @Extension(ordinal = Integer.MIN_VALUE)
 public class JenkinsHeader implements Header {
+
+    private static Logger LOGGER = Logger.getLogger(JenkinsHeader.class.getName());
 
     @Override
     public boolean isHeaderEnabled() {
         return true;
     }
+
+    @Restricted(NoExternalUse.class)
+    @CheckForNull
+    public static Header get() {
+        List<Header> headers = ExtensionList.lookup(Header.class).stream().filter(header -> header.isHeaderEnabled()).collect(Collectors.toList());
+        if (headers.size() > 0) {
+            if (headers.size() > 1) {
+                LOGGER.warning("More than one configured header. This should not happen. Serving the Jenkins default header and please review");
+            } else {
+                return headers.get(0);
+            }
+        }
+        return new JenkinsHeader();
+    }
 
 }

core/src/main/resources/lib/layout/pageHeader.jelly

@@ -1,6 +1,6 @@
 <?jelly escape-by-default='true'?>
 <j:jelly xmlns:j="jelly:core" xmlns:st="jelly:stapler" xmlns:d="jelly:define" xmlns:l="/lib/layout" xmlns:i="jelly:fmt" xmlns:x="jelly:xml">
-	<j:set var="header" value="${h.header()}" />
+	<j:invokeStatic var="header" className="jenkins.views.JenkinsHeader" method="get"/>
 	<st:include it="${header}" page="headerDocumentation.jelly"/>
 	<st:include it="${header}" page="preHeader.jelly"/>
 	<st:include it="${header}" page="headerContent.jelly"/>