  This paper investigates the role that null messages play in synchronous
systems with and without failures, and provides necessary and sufficient
conditions on the structure of protocols for information transfer and
coordination there. We start by introducing a new and more refined definition
of null messages. A generalization of message chains that allow these null
messages is provided, and is shown to be necessary and sufficient for
information transfer in reliable systems. Coping with crash failures requires a
much richer structure, since not receiving a message may be the result of the
sender's failure. We introduce a class of communication patterns called {\em
resilient message blocks}, which impose a stricter condition on protocols than
the {\em silent choirs} of Goren and Moses (2020). Such blocks are shown to be
necessary for information transfer in crash-prone systems. Moreover, they are
sufficient in several cases of interest, in which silent choirs are not.
Finally, a particular combination of resilient message blocks is shown to be
necessary and sufficient for solving the Ordered Response coordination problem.
