Merge branch 'jk/implicit-true'

Some codepaths did not correctly parse configuration variables specified with valueless "true", which has been corrected. * jk/implicit-true: fsck: handle NULL value when parsing message config trailer: handle NULL value when parsing trailer-specific config submodule: handle NULL value when parsing submodule.*.branch help: handle NULL value for alias.* config trace2: handle NULL values in tr2_sysenv config callback setup: handle NULL value when parsing extensions config: handle NULL value when parsing non-bools