Fix NullPointerException thrown by logging

When `properties` is null, this propagates a NullPointerException back
to the caller instead of cleanly reporting null like it's supposed to.

Issue introduced in Iec7ba6fc59912f44341fbe8d7f99193b9ead52f0 from the
start of this function and is fixed by just printing `object` instead
of `object.toString()`.

Test: atest AssistIntentConditionalTest
Bug: 158682298
Change-Id: Ic64f6fba65895e9facc9994f5d1a353081ab3253
(cherry picked from commit 935906e180)

services/voiceinteraction/java/com/android/server/soundtrigger/SoundTriggerService.java

@@ -697,7 +697,7 @@ public class SoundTriggerService extends SystemService {
             synchronized (mLock) {
                 ModuleProperties properties = mSoundTriggerHelper.getModuleProperties();
                 sEventLogger.log(new SoundTriggerLogger.StringEvent(
-                        "getModuleProperties(): " + properties.toString()));
+                        "getModuleProperties(): " + properties));
                 return properties;
             }
         }