util.roles: Return nil if the role has no explicit policy (fixes inheritance)
Previously, if the first inherited role had no opinion, it returned false and
prevented further consultation of other inherited roles.
This bug was found thanks to the implementation of missing test cases
identified through mutation testing.
syntax: glob
.hgignore
.luacheckcache
data
local
www_files
html/*
prosody.lua
prosody.cfg.lua
prosody.version
config.unix
*.patch
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*~
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luacov.report.out
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luacov.stats.out