Backport #10540 to jetty-10.0.x Fixed deadlock in class initialization.

jetty-http/src/main/java/org/eclipse/jetty/http/EmptyHttpFields.java

@@ -0,0 +1,45 @@
+//
+// ========================================================================
+// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+// which is available at https://www.apache.org/licenses/LICENSE-2.0.
+//
+// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+// ========================================================================
+//
+
+package org.eclipse.jetty.http;
+
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.function.Consumer;
+import java.util.stream.Stream;
+
+class EmptyHttpFields extends HttpFields.Immutable
+{
+    public EmptyHttpFields()
+    {
+        super(new HttpField[0]);
+    }
+
+    @Override
+    public Iterator<HttpField> iterator()
+    {
+        return Collections.emptyIterator();
+    }
+
+    @Override
+    public void forEach(Consumer<? super HttpField> action)
+    {
+        // no-op
+    }
+
+    @Override
+    public Stream<HttpField> stream()
+    {
+        return Stream.empty();
+    }
+}

jetty-http/src/main/java/org/eclipse/jetty/http/HttpFields.java

@@ -38,7 +38,10 @@
  */
 public interface HttpFields extends Iterable<HttpField>
 {
-    HttpFields EMPTY = build().asImmutable();
+    /**
+     * <p>A constant for an immutable and empty {@link HttpFields}.</p>
+     */
+    HttpFields EMPTY = new EmptyHttpFields();
 
     static Mutable build()
     {