Cannot read property 'type' of null

[devatwork]

Found by #349

!!! Crash found !!!
Selector: array:fold-left([1,2,3], [], function($x, $y){[$x, ?y]})
Language: XPath3.1

TypeError: Cannot read property 'type' of null
    at gs (C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:277:240)
    at C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:278:138
    at Array.reduce (<anonymous>)
    at C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:278:110
    at C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:61:434
    at Xc.E.O (C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:61:446)
    at hs (C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:278:87)
    at js.evaluate (C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:278:633)
    at ok (C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:164:458)
    at C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:219:889

[devatwork]

!!! Crash found !!!
Selector: fn:fold-left((true(), false(), false()), false(), function($a, $b) { ?a and $b })
Language: XQueryUpdate3.1

TypeError: Cannot read property 'type' of null
    at gs (C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:277:240)
    at C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:278:138
    at Array.reduce (<anonymous>)
    at C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:278:110
    at C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:61:434
    at Xc.E.O (C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:61:446)
    at hs (C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:278:87)
    at js.evaluate (C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:278:633)
    at ok (C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:164:458)
    at Object.next (C:\fontoxml\platform\fontoxpath\dist\fontoxpath.esm.js:248:483)