TypeError in getQuickInfoAtPosition for an intersection type

[mhegazy]

Reported in #7934 (comment) by @Arnavion .

class A {
    static STATIC_A: string = 'A';
    instanceA: string = 'A';
    constructor() { }
}
class B {
    static STATIC_B: string = 'B';
    instanceB: string = 'B';
}


// Define a contract to bind an instance type param (T/Z) to its static "parent" (TType/ZType)
interface ConcreteTypeOf<T> extends Function { new (...args): T; }

// Explicitly say what we are dealing with:
class MergeTypes<T, TType extends ConcreteTypeOf<T>, Z, ZType extends ConcreteTypeOf<Z>> {
    constructor(private type1: TType, private type2: ZType) { }

    // We return a constructor for T & Z and intersect static members.
    merge(): ConcreteTypeOf<T & Z> & TType & ZType {
        // Do some work to mixin the types.
        return <any>{};
    }
}

let AB = new MergeTypes<A, typeof A, B, typeof B>(A, B).merge();    // Inferred AB: ConcreteTypeOf<A & B> & typeof A & typeof B
let ab = new AB();                                                  // Inferred ab: A & B

hover over AB in new AB().

TypeError: Unable to get property 'flags' of undefined or null reference
   at buildSymbolDisplay (:16512:17)
   at Anonymous function (:45473:13)
   at mapToDisplayParts (:45459:9)
   at symbolToDisplayParts (:45472:9)
   at getSymbolDisplayPartsDocumentationAndSymbolKind (:51614:41)
   at getQuickInfoAtPosition (:51917:13)
   at Anonymous function (:55942:119)
   at simpleForwardCall (:55793:9)
   at forwardJSONCall (:55809:13)
   at forwardJSONCall (:55855:13)
   at getQuickInfoAtPosition (:55942:13)