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);
  }
  }
  }