A user of the beta release reported:
"I could not find the 'mash_generated' bbclass it inherits from. I replaced it with 'ros_superflore_generated' and it seems to work."
The spaceros preview was created before the name was selected. In order to support mash, I will need to take https://github.com/robwoolley/meta-ros/blob/spaceros-preview/meta-ros-common/classes/ros_generate_generated.bbclass and merge it across all the branches as meta-ros-common/classes/mash_generated.bbclass
Related to ros/meta-ros#1615