Excluding words in the search bar only works when there are other non-excluded words in the search bar

From the tooltip in the search bar:

Use a dash to exclude the coins matching with a word for expression.

Example: Martin Luther -King

That example works fine. What doesn't work is if you only write

-King

For example, if I use any other search criteria for issuer, metal, year, etc. (or none at all) and just want to exclude something like a denomination, it doesn't work. Little example:

Doesn't Work: https://en.numista.com/catalogue/index.php?e=frankfurt_free_imperial_city&r=-Heller&ct=coin&im1=&im2=&tb=y&tc=y&tn=y&tp=y&tt=y&cat=y&ru=&ca=3&no=&v=&i=&b=&d=&u=&a=&dg=&m=&f=&t=&w=&mt=&g=&se=&c=&wi=&sw=

Works: https://en.numista.com/catalogue/index.php?e=frankfurt_free_imperial_city&r=Frankfurt+-Heller&ct=coin&im1=&im2=&tb=y&tc=y&tn=y&tp=y&tt=y&cat=y&ru=&ca=3&no=&v=&i=&b=&d=&u=&a=&dg=&m=&f=&t=&w=&mt=&g=&se=&c=&wi=&sw=

But this trick/workaround doesn't work for all cases that might be relevant. So it would be easier if it just works without anything else in the search bar too.

Just a note: You should be careful with using negation as non-obvious items are excluded. If you search for the what you are excluding ("Frankfurt Heller") you will find many non-heller coins.

For example, this Albus is not shown if you search for “Frankfurt -Heller”: N#71916