The code was completing this pattern with a list of settable characters,
and it was possible to reach this state after completing a "ALTER
STATISTICS <name>" with SET.
Author: Vignesh C
Discussion: https://postgr.es/m/CALDaNm2HHF_371o+EeSjxDDS17Cx7d-ko2h1fLU94=ob=4_ktg@mail.gmail.com