Don't initialize last_packet_received_at to a non-time value, nil is fine.
Don't initialize last_packet_received_at to a non-time value, nil is fine.

Let the variable really express what it means.  It's current only reader
can't be meaningfully invoked before a CONNACK packet was received so there
is no need to update the reader's code.

RubyDevInc/paho.mqtt.ruby,RubyDevInc/paho.mqtt.ruby