US Treasury Bond/Notes/Bills Default?

On couple of occasions it has been mentioned in the CFA text that investment in US Govt bonds/Notes is safe and that the default risk is zero (for e.g. Question no 16 of Code of Ethics in CFA Text). Is this assumption same for any developed countrys government bonds? For e.g. UK Gilt?

Also, lets say if we advise to a client that it’s safe and default free, and if the default happenes in future? Wouldn’t this advise be a breach in code?

Its doesnt say zero it says virtually zero. While there is the possibility of default, Congress refuses to raise the debt ceiling, it is a low probablity. Default risk is a characteristic of corporate bonds, so I think the curriculum assumes no default risk for treasuries.