Describe the request

The burn-bootloader command requires the --fqbn flag. When the FQBN is missing, the CLI correctly fails, but the error message could be improved and aligned with the required programmer.

As an example, when the programmer is missing, it is clear

./arduino-cli burn-bootloader --port /dev/cu.usbserial-0001 --fqbn esp32:esp32:esp32da
Error during Upload: Missing programmer

Apply the same rule to the FQBN when it is absent, like:

./arduino-cli burn-bootloader --programmer esptool --port /dev/cu.usbserial-0001
Error during Upload: Missing FQBN

Describe the current behavior

When the FQBN is missing, the CLI interprets it as an empty and thus invalid FQBN. It might be better to treat it as missing rather than invalid:

./arduino-cli burn-bootloader --programmer esptool --port /dev/cu.usbserial-0001
Error during Upload: Invalid FQBN: not an FQBN:

Arduino CLI version

arduino-cli Version: git-snapshot Commit: 241e7d4 Date: 2025年06月26日T09:32:33Z

Operating system

macOS

Operating system version

15.5

Additional context

No response

Issue checklist

• I searched for previous requests in the issue tracker
• I verified the feature was still missing when using the nightly build
• My request contains all necessary details