Optional value exceptions have no location in plugin arguments

[bartv]

When an optional value exception is raised, it gives the location where the variable was accessed. However, if this happens in the arguments of a plugin it does not mention them:

entity Test:
end

Test.host [0:1] -- std::Host

x = Test()
std::print(x.host)

This results in:

Error: Optional variable accessed that has no value (attribute `__config__::Test.host` of `__config__::Test (instantiated at ./test.cf:7)`)

It only mentions the line x was created, not where x.host happened. For other types of statements it is correct:

entity Test:

end

Test.host [0:1] -- std::Host

x = Test()
y = x.host

Error: Optional variable accessed that has no value (attribute `__config__::Test.host` of `__config__::Test (instantiated at ./test.cf:7)`) (reported in y = x.host (./test.cf:8))