mirror of https://github.com/ARMmbed/mbed-os.git
				
				
				
			
				
					
						
							### Description
Noticed by the online compiler:
When a user has an incomplete target definition, the error is not show
to the user. That's because it's reported as a `KeyError`. This PR adds
an outer `NotSupportedException` so that the outer catch statement knows
that this is not a build system crash, but a user error.
### Pull request type
    [x] Fix
    [ ] Refactor
    [ ] Target update
    [ ] Functionality change
    [ ] Breaking change
						
					
				
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|---|---|---|
| .. | ||
| LPC.py | ||
| NCS.py | ||
| REALTEK_RTL8195AM.py | ||
| STM32_gen_PeripheralPins.py | ||
| __init__.py | ||
| lint.py | ||