Allow SearchIndex constructor to init null fields (Azure#15950)

Fixes Azure#15590

sdk/search/Azure.Search.Documents/CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## 11.2.0-beta.2 (Unreleased)
 
+### Fixed
+
+- Fixed issue calling `SearchIndexClient.GetIndexNames` that threw an exception ([#15590](https://github.com/Azure/azure-sdk-for-net/issues/15590))
 
 ## 11.2.0-beta.1 (2020-10-09)
 

sdk/search/Azure.Search.Documents/src/Indexes/Models/SearchIndex.cs

@@ -10,6 +10,9 @@ namespace Azure.Search.Documents.Indexes.Models
 {
     public partial class SearchIndex
     {
+        // Force the constructor to set the field;
+        // otherwise, when getting only names, the setter will throw.
+        [CodeGenMember("fields")]
         private IList<SearchField> _fields;
 
         [CodeGenMember("etag")]

sdk/search/Azure.Search.Documents/tests/SearchIndexClientTests.cs

@@ -286,6 +286,22 @@ public async Task GetIndexesNextPageThrows()
             Assert.ThrowsAsync<NotSupportedException>(async () => await e.MoveNextAsync());
         }
 
+        [Test]
+        public async Task GetIndexNames()
+        {
+            await using SearchResources resources = await SearchResources.GetSharedHotelsIndexAsync(this);
+
+            SearchIndexClient client = resources.GetIndexClient();
+
+            bool found = false;
+            await foreach (string name in client.GetIndexNamesAsync())
+            {
+                found |= string.Equals(resources.IndexName, name, StringComparison.InvariantCultureIgnoreCase);
+            }
+
+            Assert.IsTrue(found, "Shared index name not found");
+        }
+
         [Test]
         [SyncOnly]
         public void DeleteIndexParameterValidation()