ResourceStreamer#streamResource(Resource, String, Set) throws NPE if providedChecksum is null

The documentation of org.apache.tapestry5.internal.services.ResourceStreamer.streamResource(Resource, String, Set<Options>) states it accepts null for its second argument (providedChecksum, but it doesn't.

The org.apache.tapestry5.internal.services.ResourceStreamerImpl.streamResource(StreamableResource, String, Set<Options>), however, states that providedChecksum is allowed to be blank.

The term "blank" can be understood in different ways:

• Tools like Apache StringUtils interpret blank as "null or whitespace only"
• Java's String class has a isBlank(), which obviously requires the instance to exist

To make the behavior more obvious, the documentation should state "null or blank", and the underlying code should handle it accordingly.