hiera lookup failure

Given this /etc/puppetlabs/code/hiera.yaml --- :backends: - json :hierarchy: - "%{hostname}.%{nt_environment}.%{nt_location}" - "%{nt_type}.%{nt_environment}.%{nt_location}" - "%{nt_type}.%{nt_environment}" - "%{nt_environment}.%{nt_location}" - "%{nt_environment}" - "%{nt_location}" - world - default :logger: console # debug :json: :datadir: '/etc/puppetlabs/code/environments/%{::environment}/hieradata' # this is the default anyway and there exists /etc/puppetlabs/code/environments/prod/hieradata/sac.json, this "puppet lookup --debug icinga_servers --environment prod" produces Debug: hiera(): Looking for data source puppetmaster.ops Debug: hiera(): Looking for data source ops.sac Debug: hiera(): Looking for data source ops Debug: hiera(): Looking for data source sac Debug: hiera(): Looking for data source world Debug: hiera(): Looking for data source default (& lots more of course).
Why can't it find the /etc/puppetlabs/code/environments/prod/hieradata/sac.json file which contains the key I'm looking for ?
Puppet server 2.4 23-06-2016:
Here's an extend debug o/p Debug: Performing a hiera indirector lookup of icinga_servers with options {:variables=>Scope(Class[main]), :merge=>#>, @value_type=#]>>>]>, @options={}>} Debug: hiera(): Looking up icinga_servers in JSON backend Debug: hiera(): Looking for data source puppet4test101.ops.sac Debug: hiera(): Cannot find datafile /etc/puppetlabs/code/environments/prod/hieradata/puppet4test101.ops.sac.json, skipping Debug: hiera(): Looking for data source puppet4test.ops.sac Debug: hiera(): Cannot find datafile /etc/puppetlabs/code/environments/prod/hieradata/puppet4test.ops.sac.json, skipping Debug: hiera(): Looking for data source puppet4test.ops Debug: hiera(): Cannot find datafile /etc/puppetlabs/code/environments/prod/hieradata/puppet4test.ops.json, skipping Debug: hiera(): Looking for data source ops.sac Debug: hiera(): Looking for data source ops Debug: hiera(): Looking for data source sac HTH. As above, the file /etc/puppetlabs/code/environments/prod/hieradata/sac.json, exists and is readable. nt_location shows as 'sac' on the node by using 'facter -p'.
It seems Hiera just doesn't see that file ...
Any ideas? Chris

2016-07-05
jsonlint validates ok.
hiera -d icinga_servers -c /etc/puppetlabs/puppet/hiera.yaml nt_location=sac ::environment=prod DEBUG: 2016-07-05 01:38:52 +0000: Looking for data source .sac DEBUG: 2016-07-05 01:38:52 +0000: Cannot find datafile /etc/puppetlabs/code/environments/prod/hieradata/.sac.json, skipping DEBUG: 2016-07-05 01:38:52 +0000: Looking for data source sac DEBUG: 2016-07-05 01:38:52 +0000: Looking for data source world (Shortened o/p)
Its looking in the right place, but doesn't match :(