When paths are given in the api, they should be escaped if necessary.

For example:
props = Properties()
props["pegasus.catalog.replica.file"] = str(TOP_DIR / "replicas.yml")
props.write()

would cause a planner error if the path given was "/path/Untitled Directory/replicas.yml"

Possible solution:
import shlex
shlex.quote( "a b" )