[grid] improved exception handling when no cause is set (#11286)

improved exception handling when no cause is set

In cases where the exception thrown has no cause there was no helpful
stack trace to localize the issue.

Author: joerg1985

java/src/org/openqa/selenium/grid/router/HandleSession.java

@@ -147,8 +147,12 @@ public HttpResponse execute(HttpRequest req) {
         Throwable cause = e.getCause();
         if (cause instanceof RuntimeException) {
           throw (RuntimeException) cause;
+        } else if (cause != null) {
+          throw new RuntimeException(errorMessage, cause);
+        } else if (e instanceof RuntimeException) {
+          throw (RuntimeException) e;
         }
-        throw new RuntimeException(errorMessage, cause);
+        throw new RuntimeException(errorMessage, e);
       }
     }
   }