That is strange as “num_resources” should not be “None”. It means the parsing function at inventory time has not found any resources in your output. That is your extra line or?
If you look at the source code of this check you see that it is very old 
Your code change should also be extended for the Node detection as you system also don’t detected the three nodes, in your case also “None”.
It could help if the crm_mon status output is not the unstructured text. I don’t know how good the XML output looks like but it should be better parse-able.