Applying review suggestion

Author: eyalkoren

apm-agent-core/src/main/java/co/elastic/apm/agent/impl/transaction/TraceContext.java

@@ -713,14 +713,15 @@ public int hashCode() {
     }
 
     void setApplicationClassLoader(@Nullable ClassLoader classLoader) {
-        if (classLoader != null && !ClassLoaderUtils.isAgentClassLoader(classLoader)) {
-            WeakReference<ClassLoader> local = classLoaderWeakReferenceCache.get(classLoader);
-            if (local == null) {
-                local = new WeakReference<>(classLoader);
-                classLoaderWeakReferenceCache.putIfAbsent(classLoader, local);
-            }
-            applicationClassLoader = local;
+        if (ClassLoaderUtils.isBootstrapClassLoader(classLoader) || ClassLoaderUtils.isAgentClassLoader(classLoader)) {
+            return;
+        }
+        WeakReference<ClassLoader> local = classLoaderWeakReferenceCache.get(classLoader);
+        if (local == null) {
+            local = new WeakReference<>(classLoader);
+            classLoaderWeakReferenceCache.putIfAbsent(classLoader, local);
         }
+        applicationClassLoader = local;
     }
 
     @Nullable

apm-agent-core/src/main/java/co/elastic/apm/agent/util/ClassLoaderUtils.java

@@ -46,4 +46,8 @@ public static boolean isPersistentClassLoader(@Nullable ClassLoader classLoader)
     public static boolean isAgentClassLoader(@Nullable ClassLoader classLoader) {
         return classLoader != null && classLoader.getClass().getName().startsWith("co.elastic.apm");
     }
+
+    public static boolean isBootstrapClassLoader(@Nullable ClassLoader classLoader) {
+        return classLoader == null;
+    }
 }