Merge pull request #3737 from myasinkaji2/bugfix/npe

prevent NullPointerException when pattern is null

Author: ryanjbaxter

spring-cloud-gateway-server-mvc/src/main/java/org/springframework/cloud/gateway/server/mvc/predicate/GatewayRequestPredicates.java

@@ -272,7 +272,12 @@ public boolean test(ServerRequest request) {
 
 		@Override
 		public void accept(RequestPredicates.Visitor visitor) {
-			visitor.header(name, pattern.pattern());
+			if (pattern != null) {
+				visitor.header(name, pattern.pattern());
+			}
+			else {
+				visitor.header(name, "");
+			}
 		}
 
 		@Override