CONCEPT that is defined but not used doesn't show up in `concs`

[hanjoosten]

I have the following script:

CONTEXT Issue1487

CONCEPT Foo "This concept is not used anywhere in the script."

ENDCONTEXT

When I run the following command:

ampersand population --build-recipe Grind --verbose --output-format JSON Issue1487.adl

I get the following error:

PropertyRule for TOT concept[ConceptDef*Concept] which is defined at Concepts.adl:8:5 error:
  There is one violation of RULE "TOT concept[ConceptDef*Concept]":
    ("Foo", "Foo")