Fix androidSdk NPE (#47187)

diff --git a/packages/flutter_tools/lib/src/android/android_sdk.dart b/packages/flutter_tools/lib/src/android/android_sdk.dart
index 7e744f7..7adc6c7 100644
--- a/packages/flutter_tools/lib/src/android/android_sdk.dart
+++ b/packages/flutter_tools/lib/src/android/android_sdk.dart
@@ -55,7 +55,7 @@
   if (sdk?.latestVersion == null) {
     return os.which('adb')?.path;
   } else {
-    return sdk.adbPath;
+    return sdk?.adbPath;
   }
 }