Driving (hypothetical) example: if you have, say, a Module whose name is "" (the empty string)... that's not gonna work.
(OK that's dan-fritchman/Hdl21#176.)

There is some art to be applied regarding where to paper-over these problems versus have them produce errors. Current examples include:

• Characters we think will be illegal, e.g. in a Module named M(params) are generally replaced with underscores (M_params_).
• Everything else (I think?) goes through unmodified.

I'm not sure exactly what the right line is.
But at minimum, don't output the known-invalid stuff as though it's valid netlist-text.