Use default project resolver instead null which caused NPE when running elastic_integration integration tests.

Author: mashhurs

libs/logstash-bridge/README.md

@@ -6,3 +6,8 @@ other Elasticsearch internals.
 
 If a change is introduced in a separate Elasticsearch project that causes this project to fail,
 please consult with members of @elastic/logstash to chart a path forward.
+
+## How to build the module?
+```shell
+./gradlew :lib:logstash-bridge:build
+```

libs/logstash-bridge/src/main/java/org/elasticsearch/logstashbridge/script/ScriptServiceBridge.java

@@ -8,6 +8,7 @@
  */
 package org.elasticsearch.logstashbridge.script;
 
+import org.elasticsearch.cluster.project.DefaultProjectResolver;
 import org.elasticsearch.cluster.project.ProjectResolver;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.core.FixForMultiProject;
@@ -68,8 +69,8 @@ private static ScriptService getScriptService(final Settings settings, final Lon
             MustacheScriptEngine.NAME,
             new MustacheScriptEngine(settings)
         );
-        @FixForMultiProject // Should this be non-null?
-        final ProjectResolver projectResolver = null;
+        @FixForMultiProject // Should this be non-DefaultProjectResolver?
+        final ProjectResolver projectResolver = DefaultProjectResolver.INSTANCE;
         return new ScriptService(settings, scriptEngines, ScriptModule.CORE_CONTEXTS, timeProvider, projectResolver);
     }