Exception in read-document.ts getCollectionPartitionKeys when collection has no partitionKey saved

[dsschneidermann]

This is from working on compatibility with the CosmosDb CSharp SDK

Error logged request:

output for read-document.ts: getCollectionPartitionKeys(collection: ItemObject):
collection: {
  geospatialConfig: {},
  id: 'main',
  indexingPolicy: {
    automatic: true,
    indexingMode: 'consistent',
    includedPaths: [ [Object] ],
    excludedPaths: [],
    compositeIndexes: [],
    spatialIndexes: []
  },
  _etag: '96751c73-738f-46df-aa37-54aa6dc133b5',
  _rid: 'gAABAIAAAAM=',
  _self: '/dbs/gAABAA==/colls/gAABAIAAAAM=',
  _ts: 1604120454
}
TypeError: Cannot read property 'paths' of undefined
    at getCollectionPartitionKeys (/app/node_modules/@zeit/cosmosdb-server/lib/handler/read-document.js:15:36)
    at exports.default (/app/node_modules/@zeit/cosmosdb-server/lib/handler/read-document.js:61:32)
    at /app/node_modules/run-cosmosdb-sim/index.js:97:34
    at Server.<anonymous> (/app/node_modules/run-cosmosdb-sim/index.js:131:11)
    at Server.emit (events.js:314:20)
    at parserOnIncoming (_http_server.js:779:12)
    at HTTPParser.parserOnHeadersComplete (_http_common.js:122:17)
{
   "method":"GET",
   "url":"/dbs/devicesimulation/colls/main/docs/MasterNode",
   "docdbHeaders":[
      "x-ms-documentdb-partitionkey",
      "[]"
   ],
   "response":{
      "statusCode":500,
      "statusMessage":"Internal Server Error",
      "headers":{
         "content-type":"application/json",
         "content-location":"https://cosmosdb-sim:3000/dbs/devicesimulation/colls/main/docs/MasterNode",
         "connection":"close",
         "x-ms-activity-id":"7ac85c27-a88b-4099-bb94-e405df69f721",
         "x-ms-request-charge":"1"
      },
      "body":{
         "message":"Cannot read property 'paths' of undefined"
      }
   },
   "errorMessage":null
}

Expected result:

• Document is returned

Cause:

• Somehow the SDK or cosmosdb-server did not save an empty partition key for this document, and fails when retrieving it.

Proposed fix by this PR:

• Add a conditional check on collection.partitionKey and return an empty list.