Docs are showing an empty dictionary in places

[phlax]

description

seems like there is an issue with protodoc that is causing an empty dictionarry to be added to some of the generated docs

for example:

https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/filter/thrift/router/v2alpha1/router.proto#config-filter-thrift-router-v2alpha1-router

[phlax]

@antoniovicente ive added a "fix" for this in #15983

not sure if this is the best fix - it just stops it from outputting the empty dict - im wondering if you had a better idea here