"Object model not specified for time X" #1
Description
Currently if generating a network with a copied operation model, the user needs to specify the same finishing time as whichever corresponding line in the operation model time that they want to finish on. Otherwise the while loop in the execute() method within Grow will go round an extra iteration, resulting in trying to add nodes/edges with an unspecified operation model, throwing an error. Can do a quick fix but would be nice to do something more thoughtful.