Fix IllegalStateException when starting a trace before Firebase init (#6371)

Fix IllegalStateException when starting a trace before Firebase
initializes.

This can happen if you manually initialize Firebase. See #4693

Author: mrober

firebase-perf/CHANGELOG.md

@@ -1,4 +1,5 @@
 # Unreleased
+* [fixed] Fix IllegalStateException when starting a trace before Firebase initializes.
 * [changed] Updated protobuf dependency to `3.25.5` to fix
   [CVE-2024-7254](https://github.com/advisories/GHSA-735f-pc8j-v9w8).
 

firebase-perf/src/main/java/com/google/firebase/perf/config/RemoteConfigManager.java

@@ -88,7 +88,13 @@ private RemoteConfigManager() {
   @VisibleForTesting
   @SuppressWarnings("FirebaseUseExplicitDependencies")
   static long getInitialStartupMillis() {
-    StartupTime startupTime = FirebaseApp.getInstance().get(StartupTime.class);
+    StartupTime startupTime = null;
+    try {
+      startupTime = FirebaseApp.getInstance().get(StartupTime.class);
+    } catch (IllegalStateException ex) {
+      // This can happen if you start a trace before Firebase is init
+      logger.debug("Unable to get StartupTime instance.");
+    }
     if (startupTime != null) {
       return startupTime.getEpochMillis();
     } else {