Abort when trying to use {{.}} or {{{.}}} while not iterating

"one": True,"two": True,

root@OH-WIN:/northern.tech/cfengine/core# cat test.cf
bundle agent main
{
  vars:
    "c" data => '[ "one", "two" ]';
    "c2" string => string_mustache( '"{{{.}}}": True,', c );
  reports:
    "$(c2)";
}
root@OH-WIN:/northern.tech/cfengine/core# /var/cfengine/bin/cf-agent -KI test.cf
cf-promises: mustache.c:495: RenderVariable: Assertion `false' failed.
Aborted
   error: Policy failed validation with command '"/var/cfengine/bin/cf-promises" -c "test.cf"'
   error: Failsafe condition triggered. Interactive session detected, skipping failsafe.cf execution.
   error: Error reading CFEngine policy. Exiting...
root@OH-WIN:/northern.tech/cfengine/core#