Write a test for omiting blank displayname and avatar_url info from m.room.member events

[aaronraimist]

matrix-org/synapse#7497

Probably goes in https://github.com/matrix-org/sytest/blob/cab0f6b3a0ae8c8324f5c8ab609ac6286da178ca/tests/10apidoc/10profile-displayname.pl and https://github.com/matrix-org/sytest/blob/cab0f6b3a0ae8c8324f5c8ab609ac6286da178ca/tests/10apidoc/11profile-avatar_url.pl

[chavanarjun]

what should I do here

[clokep]

This should probably be done in complement now, not sytest?