Unhandled AttributeError in expressions for non-existent objects

If an expression (using contexts) contains a non-existent object, an unhandled AttributeError is displayed in the logs instead of the ValueError.

For example, it happens when a rule in the quality gate definition contains the following scope:

scope: test.technology.abcdefgh == 'cypress'

(technology parameter is a string, not an object, and cannot contain any other parameter)

This case needs to be handled.