Fixed null reference exception when Android SDK path not set.

If the Android SDK path is not set the Android Resolver now
reports an error rather and fails resolution rather than throwing
a null reference exception.

Bug: 67596956
Change-Id: I75517a7d216d9ef74f8c184e89de780818917448

Author: Stewart Miles

CHANGELOG.md

@@ -1,3 +1,8 @@
+# Version 1.2.62 - TBD
+## Bug Fixes
+* Fixed Android Resolver throwing NullReferenceException when the Android SDK
+  path isn't set.
+
 # Version 1.2.61 - Jan 22, 2017
 ## Bug Fixes
 * Fixed Android Resolver reporting non-existent conflicting dependencies when

source/PlayServicesResolver/src/ResolverVer1_1.cs

@@ -845,6 +845,19 @@ private void DoResolutionUnsafe(
         {
             // Cache the setting as it can only be queried from the main thread.
             var sdkPath = svcSupport.SDK;
+            // If the Android SDK path isn't set or doesn't exist report an error.
+            if (String.IsNullOrEmpty(sdkPath) || !Directory.Exists(sdkPath)) {
+                PlayServicesResolver.Log(String.Format(
+                    "Android dependency resolution failed, your application will probably " +
+                    "not run.\n\n" +
+                    "Android SDK path must be set to a valid directory ({0})\n" +
+                    "This must be configured in the 'Preference > External Tools > Android SDK'\n" +
+                    "menu option.\n", String.IsNullOrEmpty(sdkPath) ? "{none}" : sdkPath),
+                    level: LogLevel.Error);
+                resolutionComplete();
+                return;
+            }
+
             System.Action resolve = () => {
                 PlayServicesResolver.Log("Performing Android Dependency Resolution",
                                          LogLevel.Verbose);