I guess that adb was unable to push the public key to the device, and thus the device could never show the authorization dialog. It defaults to charging mode. This bit will involve a little experimentation but choose Transfer files and then run the adb devices command. If it still returns the device as unauthorized , repeat the process but this time around choose Transfer Photos. One of these connection types will fix the ADB device unauthorized message.
It is now a valuable resource for people who want to make the most of their mobile devices, from customizing the look and feel to adding new functionality. Due to different processor, there is change in id. That cause trouble in connecting device in adb. Instead driver are install ,but u cant interface with ur device. So here a simple tutorial to get.
Bei mir kam es zur oben stehenden Fehlermeldung als ich mein LeEco Le Max per ADB in den Bootloader Mode starten wollte. Nach dem Befehl adb reboot bootloader kam es zur Fehlermeldung error: device ‚(Null)‘ not found. Zu dieser Meldung kann es kommen, wenn der USB Debugging Mode deaktiviert ist oder der ADB Driver nicht installiert ist. Check and uncheck the USB Debugging option in the device.
If that doesn’t work unplug and plug in the USB a couple of times. At some point, the device should show a message box to ask you to authorize the computer.