"IllegalArgumentException: blank element" by GraphQLWebsocketServlet.modifyHandshake (in jetty 12.0.16)

[sitepark-veltrup]

After updating to Jetty 12.0.16 I get the following exception:

Caused by: java.lang.IllegalArgumentException: blank element
	at org.eclipse.jetty.http.HttpField$MultiHttpField.buildValue(HttpField.java:741) ~[jetty-http-12.0.16.jar:12.0.16]
	at org.eclipse.jetty.http.HttpField$MultiHttpField.<init>(HttpField.java:731) ~[jetty-http-12.0.16.jar:12.0.16]
	at org.eclipse.jetty.http.HttpFields$Mutable.put(HttpFields.java:1312) ~[jetty-http-12.0.16.jar:12.0.16]
	at org.eclipse.jetty.websocket.core.server.internal.WebSocketHttpFieldsWrapper.put(WebSocketHttpFieldsWrapper.java:128) ~[jetty-websocket-core-server-12.0.16.jar:12.0.16]
	at org.eclipse.jetty.http.HttpFieldsMap$Mutable.put(HttpFieldsMap.java:85) ~[jetty-http-12.0.16.jar:12.0.16]
	at org.eclipse.jetty.http.HttpFieldsMap$Mutable.put(HttpFieldsMap.java:39) ~[jetty-http-12.0.16.jar:12.0.16]
	at graphql.kickstart.servlet.GraphQLWebsocketServlet.modifyHandshake(GraphQLWebsocketServlet.java:216) ~[graphql-java-servlet-16.0.0.jar:?]
       ...

The reason for this is probably this adjustment in the Jetty. It is no longer permitted to set empty header values here.

However, this is the case here.

Because here the protocol list is created and the fallbackSubscriptionProtocolFactory is used to create a factory with an empty string as the protocol.

[federicorispo]

@sitepark-veltrup Thank you for the time spent opening this bug! We will investigate it as soon as possible.