Internal server error when creating existing smart_class_variable override via foreman_api

hi,

foreman version : 1.4.4
foreman_api version: 0.1.11

when i try to create an already existing smart_class_parameter override
value via the foreman_api i do get a 500 internal server error instead
of a useful failure message.

the example code and the stack trace from the foreman production log is
here:

maybe i'm using the foreman_api in the wrong way, i just started using
it. i was just expecting some kind of 4xx failure code, not an internal
server error.

should i open a bug report?

thanks for you help
toni