String.length NPE

gistfile1.txt

  1> 	at com.carrotsearch.randomizedtesting.ThreadLeakControl$StatementRunner.run(ThreadLeakControl.java:367) ~[randomizedtesting-runner-2.4.0.jar:?]
  1> 	at java.lang.Thread.run(Thread.java:745) ~[?:1.8.0_92-internal]
  1> Caused by: java.lang.NullPointerException
  1> 	at java.lang.String.length(String.java:623) ~[?:1.8.0_92-internal]
  1> 	at org.elasticsearch.common.regex.Regex.simpleMatch(Regex.java:116) ~[main/:?] --> https://github.com/elastic/elasticsearch/blob/master/core/src/main/java/org/elasticsearch/common/regex/Regex.java#L116
  1> 	at org.elasticsearch.common.regex.Regex.simpleMatch(Regex.java:133) ~[main/:?] 
  1> 	at org.elasticsearch.transport.TransportService.shouldTraceAction(TransportService.java:664) ~[main/:?]
  1> 	at org.elasticsearch.transport.TransportService.access$900(TransportService.java:73) ~[main/:?]
  1> 	at org.elasticsearch.transport.TransportService$Adapter.onRequestSent(TransportService.java:740) ~[main/:?]
  1> 	at org.elasticsearch.transport.TcpTransport.lambda$sendRequestToChannel$12(TcpTransport.java:1036) ~[main/:?]
  1> 	at org.elasticsearch.transport.MockTcpTransport.sendMessage(MockTcpTransport.java:253) ~[framework-6.0.0-alpha1-SNAPSHOT.jar:?]
  1> 	at org.elasticsearch.transport.MockTcpTransport.sendMessage(MockTcpTransport.java:72) ~[framework-6.0.0-alpha1-SNAPSHOT.jar:?]
  1> 	at org.elasticsearch.transport.TcpTransport.internalSendMessage(TcpTransport.java:1057) ~[main/:?]
  1> 	at org.elasticsearch.transport.TcpTransport.sendRequestToChannel(TcpTransport.java:1039) ~[main/:?]
  1> 	at org.elasticsearch.transport.TcpTransport.executeHandshake(TcpTransport.java:1554) ~[main/:?]
  2> REPRODUCE WITH: gradle :core:integTest -Dtests.seed=AAC4994A2F837C0B -Dtests.class=org.elasticsearch.indices.settings.UpdateSettingsIT -Dtests.method="testUpdateAutoThrottleSettings" -Dtests.security.manager=true -Dtests.locale=it -Dtests.timezone=Africa/Banjul