Host details

Hi

i am using 6.8 metricbeat and server is 7.12 .
a. add host metricset and got error , so enable add_host_metadata : ~
b . as per documentation . add_host_metadata it should collect
"host":{
"architecture":"x86_64",
"name":"example-host",
"id":"",
"os":{
"family":"darwin",
"build":"16G1212",
"platform":"darwin",
"version":"10.12.6",
"name":"Mac OS X"
},

but it is not having os.build details and also .i see os.family & other fields are blank
what command it is using internally or is there any known bugs