Don't throw a NPE in SharedLog#e

Some DhcpServer error code paths could cause a NPE, when the logError
callback was called without an exception. Allowing SharedLog#e to be
called with a null Throwable is less error-prone.

Bug: b/109584964
Test: atest FrameworksNetTests
Change-Id: Idbcdd330a9d1951b27aaf525aaf12e52e102872c

2 files changed, 16 insertions, 3 deletions

diff --git a/services/net/java/android/net/util/SharedLog.java b/services/net/java/android/net/util/SharedLog.java
index f7bf393f367b..5a73a4e492ee 100644
--- a/services/net/java/android/net/util/SharedLog.java
+++ b/services/net/java/android/net/util/SharedLog.java
@@ -17,6 +17,7 @@
 package android.net.util;
 
 import android.annotation.NonNull;
+import android.annotation.Nullable;
 import android.text.TextUtils;
 import android.util.LocalLog;
 import android.util.Log;
@@ -92,10 +93,17 @@ public class SharedLog {
     }
 
     /**
-     * Log an error due to an exception, with the exception stacktrace.
+     * Log an error due to an exception, with the exception stacktrace if provided.
+     *
+     * <p>The error and exception message appear in the shared log, but the stacktrace is only
+     * logged in general log output (logcat).
      */
-    public void e(@NonNull String msg, @NonNull Throwable e) {
-        Log.e(mTag, record(Category.ERROR, msg + ": " + e.getMessage()), e);
+    public void e(@NonNull String msg, @Nullable Throwable exception) {
+        if (exception == null) {
+            e(msg);
+            return;
+        }
+        Log.e(mTag, record(Category.ERROR, msg + ": " + exception.getMessage()), exception);
     }
 
     public void i(String msg) {
diff --git a/tests/net/java/android/net/util/SharedLogTest.java b/tests/net/java/android/net/util/SharedLogTest.java
index d46facfaba06..86048604e95f 100644
--- a/tests/net/java/android/net/util/SharedLogTest.java
+++ b/tests/net/java/android/net/util/SharedLogTest.java
@@ -44,6 +44,8 @@ public class SharedLogTest {
         final SharedLog logLevel2a = logTop.forSubComponent("twoA");
         final SharedLog logLevel2b = logTop.forSubComponent("twoB");
         logLevel2b.e("2b or not 2b");
+        logLevel2b.e("No exception", null);
+        logLevel2b.e("Wait, here's one", new Exception("Test"));
         logLevel2a.w("second post?");
 
         final SharedLog logLevel3 = logLevel2a.forSubComponent("three");
@@ -54,6 +56,9 @@ public class SharedLogTest {
         final String[] expected = {
             " - MARK first post!",
             " - [twoB] ERROR 2b or not 2b",
+            " - [twoB] ERROR No exception",
+            // No stacktrace in shared log, only in logcat
+            " - [twoB] ERROR Wait, here's one: Test",
             " - [twoA] WARN second post?",
             " - still logging",
             " - [twoA.three] 3 >> 2",