What does it mean that "if null, the name of input will be set as the path"?
If your path argument points to a directory or a single file, and if you specify no argument for the input variable, the filenames resulting from your first argument will be adopted as database paths.
If you run the command "ADD myfile.xml", the input argument will be null. If you run "ADD TO /db/path myfile.xml", input will be "/db/path".