It is impossible to dump to directory a collection which matches one of the the reserved windows filenames (e.g. "con" or "aux"): https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file#naming-conventions

On Windows 10, aux, prn, com1, lpt1 all produce the following error:

Failed: error dumping metadata: error creating metadata file dump\test\lpt1.metadata.json: open dump\test\lpt1.metadata.json: The system cannot find the file specified.

con produces this different error:

Failed: error dumping metadata: error creating metadata file dump\test\con.metadata.json: open dump\test\con.metadata.json: The parameter is incorrect.

nul worked as normal.

It is possible to dump to an archive instead, so there is a simple workaround.

However, the error messages for these collections are unclear. As a small enhancement might be to provide a clearer error message. We could also dump any collections with windows reserved names using the same method we use for long collection names (i.e. append a hash to the filename).