Address possibly nil country codes (#3975)

* Address possibly nil country codes

* Update CHANGELOG

Author: mikehaney24

GoogleDataTransportCCTSupport/CHANGELOG.md

@@ -2,6 +2,7 @@
 - Updates GDT dependency to improve backgrounding logic.
 - Reduces requests for background task creation. (#3893)
 - Fix unbalanced background task creation in GDTCCTUploader. (#3838)
+- Fixes a nil argument being passed to GDTCCTEncodeString. (#3893)
 
 # v1.1.0
 - Updates GDT dependency to GDTCOR prefixed version.

GoogleDataTransportCCTSupport/GDTCCTLibrary/GDTCCTNanopbHelpers.m

@@ -162,7 +162,10 @@ gdt_cct_IosClientInfo GDTCCTConstructiOSClientInfo() {
   if (version) {
     iOSClientInfo.application_build = GDTCCTEncodeString(version);
   }
-  iOSClientInfo.country = GDTCCTEncodeString([locale objectForKey:NSLocaleCountryCode]);
+  NSString *countryCode = [locale objectForKey:NSLocaleCountryCode];
+  if (countryCode) {
+    iOSClientInfo.country = GDTCCTEncodeString([locale objectForKey:NSLocaleCountryCode]);
+  }
   iOSClientInfo.model = GDTCCTEncodeString(device.model);
   NSString *languageCode = bundle.preferredLocalizations.firstObject;
   iOSClientInfo.language_code =