Rule.output is sometimes undefined for the GenericGCC applicationLinker rule

ERROR: /share/qbs/modules/cpp/GenericGCC.qbs:255 evaluating prepare script: TypeError: Result of expression 'output' [undefined] is not an object.

Reproducible every time with my project when building from scratch. Building a second time with the already-existing build graph (may) complete successfully.

Note that all this only occurs with the 'release' build variant.