TypeError: Cannot read property 'initializer' of undefined in 'isAtTriggerLocation' during 'getApplicableRefactors'

[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: 2.7.1
VSCode Version 1.20.0-insider
command requested: getApplicableRefactors
hitting sessions: 557
proportion of all sessions: 0.0020793435695273506
five line hash: 4109e84fe75a41b3535e2d9412a42d8e
stack

TypeError: Cannot read property 'initializer' of undefined
    at isAtTriggerLocation (tsserver.js:79994:79)
    at isAtTriggerLocation (tsserver.js:79999:44)
    at Object.getAvailableActions (tsserver.js:79971:21)
    at unknown (tsserver.js:77085:128)
    at getIterator (tsserver.js:1733:23)
    at Object.next (tsserver.js:1728:35)
    at Object.arrayFrom (tsserver.js:2267:32)
    at Object.getApplicableRefactors (tsserver.js:77084:23)
    at Object.getApplicableRefactors (tsserver.js:83299:32)
    at IOSession.Session.getApplicableRefactors (tsserver.js:90156:53)
    at Session.handlers.ts.createMapFromTemplate._a.(anonymous function) (tsserver.js:89112:61)
    at unknown (tsserver.js:90355:88)
    at IOSession.Session.executeWithRequestId (tsserver.js:90346:28)
    at IOSession.Session.executeCommand (tsserver.js:90355:33)
    at IOSession.Session.onMessage (tsserver.js:90375:35)
    at Interface.<anonymous> (tsserver.js:91576:27)
    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)

[aozgaa]

This issue reproduced in the following context:
TypeScript Version Prefix: 2.7.2
VSCode Version 1.21.0-insider
command requested: getApplicableRefactors
hitting sessions: 105
proportion of all sessions: 0.002155659118438071
stack

TypeError: Cannot read property 'initializer' of undefined
    at isAtTriggerLocation (tsserver.js:80192:79)
    at isAtTriggerLocation (tsserver.js:80197:44)
    at Object.getAvailableActions (tsserver.js:80169:21)
    at unknown (tsserver.js:77283:128)
    at getIterator (tsserver.js:1734:23)
    at Object.next (tsserver.js:1729:35)
    at Object.arrayFrom (tsserver.js:2268:32)
    at Object.getApplicableRefactors (tsserver.js:77282:23)
    at Object.getApplicableRefactors (tsserver.js:83497:32)
    at IOSession.Session.getApplicableRefactors (tsserver.js:90354:53)
    at Session.handlers.ts.createMapFromTemplate._a.(anonymous function) (tsserver.js:89310:61)
    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)