TypeError: Cannot read property 'getChildren' of undefined in 'Object.findChildOfKind' during 'completions'

[aozgaa]

This issue comes from crash dumps in telemetry. We've tried to de-duplicate issues on a best-effort basis, comparing the sequence of methods called and the command requested while ignoring line numbers.
TypeScript Version Prefix: 2.7.2
VSCode Version 1.20.1
command requested: completions
hitting sessions: 409
proportion of all sessions: 0.029151817533856022
five line hash: ebebd291ec97e3f9774847e65d533f4c
stack

TypeError: Cannot read property 'getChildren' of undefined
    at Object.findChildOfKind (tsserver.js:64706:25)
    at createCompletionEntry (tsserver.js:67095:34)
    at getCompletionEntriesFromSymbols (tsserver.js:67142:29)
    at completionInfoFromData (tsserver.js:67047:17)
    at Object.getCompletionsAtPosition (tsserver.js:67011:28)
    at Object.getCompletionsAtPosition (tsserver.js:83037:35)
    at IOSession.Session.getCompletions (tsserver.js:90076:64)
    at Session.handlers.ts.createMapFromTemplate._a.(anonymous function) (tsserver.js:89177:61)
    at unknown (tsserver.js:90553:88)
    at IOSession.Session.executeWithRequestId (tsserver.js:90544:28)
    at IOSession.Session.executeCommand (tsserver.js:90553:33)
    at IOSession.Session.onMessage (tsserver.js:90573:35)
    at Interface.<anonymous> (tsserver.js:91774:27)
    at emitOne (events.js:96:13)
    at Interface.emit (events.js:191:7)
    at Interface._onLine (readline.js:241:10)
    at Interface._normalWrite (readline.js:384:12)
    at Socket.ondata (readline.js:101:10)
    at emitOne (events.js:96:13)
    at Socket.emit (events.js:191:7)
    at readableAddChunk (_stream_readable.js:178:18)
    at Socket.Readable.push (_stream_readable.js:136:10)
    at Pipe.onread (net.js:560:20)

[ghost]

Duplicate of #21790