Error when setting surrounding timerange to milliseconds.

Hello,

I'm setting surrounding timerange to 100 milliseconds (PT0.1S).
Looks like web interface understands the format, because it automatically displays "100 milliseconds".


But hitting 'Save', shows an error:

Here's also error from /var/log/graylog-server/server.log:

`2021-01-28T10:50:44.536+02:00 ERROR [ClusterConfigResource] Couldn't write cluster config "org.graylog2.indexer.searches.SearchesClusterConfig".
java.lang.IllegalArgumentException: Invalid BSON field name PT0.100S
at org.bson.AbstractBsonWriter.writeName(AbstractBsonWriter.java:532) ~[graylog.jar:?]
at com.mongodb.internal.connection.BsonWriterDecorator.writeName(BsonWriterDecorator.java:193) ~[graylog.jar:?]
at com.mongodb.DBObjectCodec.encodeMap(DBObjectCodec.java:255) ~[graylog.jar:?]
at com.mongodb.DBObjectCodec.writeValue(DBObjectCodec.java:232) ~[graylog.jar:?]
at com.mongodb.DBObjectCodec.encodeMap(DBObjectCodec.java:256) ~[graylog.jar:?]
at com.mongodb.DBObjectCodec.writeValue(DBObjectCodec.java:232) ~[graylog.jar:?]
at com.mongodb.DBObjectCodec.encode(DBObjectCodec.java:159) ~[graylog.jar:?]
at com.mongodb.DBObjectCodec.encode(DBObjectCodec.java:67) ~[graylog.jar:?]
`

Is it a bug that needs some fixing? Or i can set milliseconds for surrounding messages somewhere else?

Running Graylog 4.0.1+6a0cc0b on Ubuntu 18.04.5 LTS.