Index API returns json with unexpected values

Using the REST API to query GL index sets returns json output with unexpected key values, these also prevent an updated config json from being applied via curl until removed manually.

## Expected Behavior
`curl -u [TOKEN]:token -XGET localhost:9000/api/system/indices/index_sets/[Index_set_id]`

output
working JSON config block

## Current Behavior
returns JSON with unexpected `AutoValue_` entries
`{"id":"INDEX_SET ID","title":"Default index set","description":"The Graylog default index set","index_prefix":"graylog","shards":4,"replicas":1,"rotation_strategy_class":"org.graylog2.indexer.rotation.strategies.SizeBasedRotationStrategy","rotation_strategy":{"type":"org.graylog2.indexer.rotation.strategies.AutoValue_SizeBasedRotationStrategyConfig","type":"org.graylog2.indexer.rotation.strategies.SizeBasedRotationStrategyConfig","max_size":1000000000},"retention_strategy_class":"org.graylog2.indexer.retention.strategies.DeletionRetentionStrategy","retention_strategy":{"type":"org.graylog2.indexer.retention.strategies.AutoValue_DeletionRetentionStrategyConfig","type":"org.graylog2.indexer.retention.strategies.DeletionRetentionStrategyConfig","max_number_of_indices":30},"creation_date":"2020-02-04T12:08:29.134Z","index_analyzer":"standard","index_optimization_max_num_segments":1,"index_optimization_disabled":true,"field_type_refresh_interval":5000,"index_template_type":null,"default":true,"writable":true}`

See unexpected `type` values within `rotation_strategy` and `retention_strategy`

## Your Environment
* Graylog Version: 4.0.7