SearchIndexClient.GetIndexNames throws

[bleroy]

Describe the bug
Calling SearchIndexClient.GetIndexNames throws an ArgumentNullException with the message "Fields cannot be null. To clear values, call Clear. (Parameter 'value')".

Expected behavior
The method should return the list of index names.

Actual behavior (include Exception or Stack Trace)
Calling SearchIndexClient.GetIndexNames throws an ArgumentNullException with the message "Fields cannot be null. To clear values, call Clear. (Parameter 'value')".

The reason this is happening is that GetIndexNames calls IndexesClient.List with Constants.NameKey, which results in a JSON document missing all properties except for the name of the index. Attempting to deserialize this then fails because fields are required, and are missing (despite definitely existing on the actual indexes) in the JSON getting passed in.

The implementation of GetIndexNames and GetIndexNamesAsync should either use a different new method on the IndexerRestClient that doesn't attempt to deserialize indexes but just extracts the name that are needed, or should Constants.All before it does the deserialization like GetIndexes does.

Workaround
Use SearchIndexClient.GetIndexes(serviceName, credentials).Select(idx => idx.Name) instead.

To Reproduce
Call SearchIndexClient.GetIndexNames.

Environment:

• Name and version of the Library package used: Azure.Search.Documents 11.1.1
• Hosting platform or OS and .NET runtime version (dotnet --info output for .NET Core projects): .NET Core 3.1
• IDE and version : Visual Studio 16.8.0 Preview 3.2

[heaths]

Since we're close to code complete and I have another issue I'm working on, I'm moving this to November. If we need this for October 6th, please let me know ASAP.