Cannot create index due to missing key

[alhell]

Library name and version

Azure.Search.Service 10.1.0

Describe the bug

Cannot create index.

public class DocumentIndex
{
    [SimpleField(IsKey = true)]
    public string metadata_storage_path { get; set; }

.
.
.
.
.
}

Error
Microsoft.Rest.Azure.CloudException: 'The request is invalid. Details: index : Found 0 key fields in index 'index'. Each index must have exactly one key field.'

Expected behavior

Index Created

Actual behavior

Error
Microsoft.Rest.Azure.CloudException: 'The request is invalid. Details: index : Found 0 key fields in index 'index'. Each index must have exactly one key field.'

Reproduction Steps

foreach (var index in Indexes.IndexList)
{

  var definition = new Index()
  {
      Name = index,
      Fields = FieldBuilder.BuildForType<DocumentIndex>()
  };
  await client.Indexes.CreateAsync(definition);

}

Environment

No response

[github-actions]

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