Memory Model Analysis: Uncaught TypeError: Cannot read property '1' of null at extractIdFromClasses (mmGraphUtilService.js:113)

Consider this program: https://pseuco.com/#/edit/remote/4uqpoy8vxhe237gl0yj1

Try forcing the first read to any value. Adding the constraint crashes:

Uncaught TypeError: Cannot read property '1' of null
    at Or (app.js:177)
    at SVGGElement.<anonymous> (app.js:177)
    at SVGGElement.<anonymous> (app.js:177)

Notice that this program is fine: https://pseuco.com/#/edit/remote/7400gygvgeblo61olgoz

This is already broken in e1446276.