From the perldoc of Net::SNMP:

get_request() - send a SNMP get-request to the remote agent
     $result = $session->get_request(
                   [-callback        => sub {},]     # non-blocking
                   [-delay           => $seconds,]   # non-blocking
                   [-contextengineid => $engine_id,] # v3
                   [-contextname     => $name,]      # v3
                   -varbindlist      => \@oids,
               );

[...]

  A reference to a hash is returned in blocking mode 
  which contains the contents of the VarBindList. 
  In non-blocking mode, a true value is returned when 
  no error has occurred. In either mode, the undefined 
  value is returned when an error has occurred. The 
  "error()" method may be used to determine the cause 
  of the failure.
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I see you're using 'nonblocking' mode in your call to session() so you're getting a "TRUE" value returned as per the documented operation. Try removing the '-nonblocking => 1' line from the call to session() and see what happens.