Today the Nationals announced the trade of LHP Danny Rosenbaum for AAA veteran Dan Butler, as part of an offseason push to replenish the upper minors with catchers.
Rosenbaum was a 2009 pick out of Xavier University who quickly established himself as a workhorse, throwing 140+ innings in his first three full seasons (2011-2013). That also earned him a Rule 5 look-see during the 2012-13 offseason before developing Nationals elbow last spring. He was expected to spend 2015 rehabbing in the GCL and perhaps Auburn before becoming a six-year free agent.
As noted in the link above, Roberts is one of several minor-league veteran catchers (Steven Lerud, Omir Santos) added in the wake of the departures of 40-man backstop Jhonatan Solano as well as AA/AAA reserves Brian Jeroloman and Mitch Canham.