26ca748…-vendor.js:41 TypeError: Cannot read property 'toJSON' of undefined
    at N.n.render (26ca748…-duolingo.js:9)
    at success (26ca748…-duolingo.js:3)
    at t.success (26ca748…-vendor.js:5)
    at Object.i.success (26ca748…-vendor.js:5)
    at Object.a (26ca748…-vendor.js:41)
    at O (26ca748…-vendor.js:5)
    at Object.n [as success] (26ca748…-vendor.js:5)
    at c (26ca748…-vendor.js:2)
    at Object.fireWith [as resolveWith] (26ca748…-vendor.js:2)
    at n (26ca748…-vendor.js:4)