@NonNull
    @Override
    public String toString() {
        return "Destination address: " + Integer.toHexString(dst) +
                "\nCount Log: " + Integer.toHexString(countLog) +
                "\nPeriod Log: " + Integer.toHexString(periodLog) +
                "\nTTL: " + ttl +
                "\nFeatures: " + features == null ? "null" : features.toString() +
                "\nNet key index: " + Integer.toHexString(netKeyIndex);
    }
Heartbeat subscription.

@param dst         Destination address identifies the Heartbeat Publication
                   destination where the address can only be an unassigned address,
                   unicast address or a group address. All other values are prohibited.
@param countLog    Number of Heartbeat messages to be sent.
@param periodLog   Period for sending Heartbeat messages.
@param ttl         TTL to be used when sending Heartbeat messages.
@param features    Bit field indicating features that trigger Heartbeat messages when changed.
@param netKeyIndex Net key index.
mesh/src/main/java/no/nordicsemi/android/mesh/utils/HeartbeatPublication.java