When the system property jdk.internal.httpclient.debug is set to true, the HttpClient implementation generates internal log messages. One of the log message has an incorrect format specifier which results in the following log message:

> SelectorAttachment Registering %s for %d (%s)

The %s, %d and %s are expected to be replaced with relevant values but because a String is being passed for the %d specifier, the conversion fails which results in the message being printed verbatim.