Update getEmergencyAssistancePackageName's return to be @Nullable.

This change fixes failing CTS tests on Android Auto targets.

Bug: 325709685
Test: atest TelephonyManagerTest
Change-Id: I4c9add93d084b2cf1b55fa76e8781237045fe852

core/api/system-current.txt

@@ -15343,7 +15343,7 @@ package android.telephony {
     method @Deprecated public boolean getDataEnabled(int);
     method @Nullable @RequiresPermission(android.Manifest.permission.INTERACT_ACROSS_USERS) public android.content.ComponentName getDefaultRespondViaMessageApplication();
     method @Nullable @RequiresPermission(android.Manifest.permission.READ_PHONE_STATE) public String getDeviceSoftwareVersion(int);
-    method @FlaggedApi("android.permission.flags.get_emergency_role_holder_api_enabled") @NonNull @RequiresPermission(android.Manifest.permission.READ_PRIVILEGED_PHONE_STATE) public String getEmergencyAssistancePackageName();
+    method @FlaggedApi("android.permission.flags.get_emergency_role_holder_api_enabled") @Nullable @RequiresPermission(android.Manifest.permission.READ_PRIVILEGED_PHONE_STATE) public String getEmergencyAssistancePackageName();
     method @RequiresPermission(android.Manifest.permission.READ_PRIVILEGED_PHONE_STATE) public boolean getEmergencyCallbackMode();
     method @RequiresPermission(android.Manifest.permission.READ_PRIVILEGED_PHONE_STATE) public int getEmergencyNumberDbVersion();
     method @Nullable @RequiresPermission(android.Manifest.permission.READ_PRIVILEGED_PHONE_STATE) public String getIsimDomain();

telephony/java/android/telephony/TelephonyManager.java

@@ -15021,16 +15021,15 @@ public class TelephonyManager {
      */
     @RequiresPermission(android.Manifest.permission.READ_PRIVILEGED_PHONE_STATE)
     @FlaggedApi(android.permission.flags.Flags.FLAG_GET_EMERGENCY_ROLE_HOLDER_API_ENABLED)
-    @NonNull
+    @Nullable
     @SystemApi
     public String getEmergencyAssistancePackageName() {
         if (!isEmergencyAssistanceEnabled() || !isVoiceCapable()) {
             throw new IllegalStateException("isEmergencyAssistanceEnabled() is false or device"
                 + " not voice capable.");
         }
-        String emergencyRole = mContext.getSystemService(RoleManager.class)
+        return mContext.getSystemService(RoleManager.class)
                 .getEmergencyRoleHolder(mContext.getUserId());
-        return Objects.requireNonNull(emergencyRole, "Emergency role holder must not be null");
     }
     /**