public static boolean isValidHeartbeatSubscriptionSource(final int address) {
        if (isValidUnassignedAddress(address) || isValidUnicastAddress(address))
            return true;
        else
            throw new IllegalArgumentException("Source address must be an unassigned address or a unicast address!");
    }
Validates if the address is a valid Heartbeat subscription source.
A valid address shall be an unassigned address, a unicast address.
All other values are Prohibited.

@param address address
@return true if valid or false otherwise.
@throws IllegalArgumentException if the address is not the unassigned address or a unicast address.
mesh/src/main/java/no/nordicsemi/android/mesh/utils/MeshAddress.java