The introduction of issync? in the sensu_check type for the handlers and
dependencies properties introduced an assumption that the values sourced
are always arrays, yet :array_matching is set.

In the event that an empty array is passed to the property within
Puppet, Puppet will match this against an non-existing (nil) value and
so will not write out the key/value pair on flush. When re-reading the
file to analyze for changes, a nil value is loaded in return, but a
NilClass has no sort method and so compilation of the catalog fails.

This change sets the defaults within the type's JSON provider to always
return an empty array unless something else is configured, preventing
the issync? method from raising an exception on NilClass's.