Dashboard migration issue from 6.1 dashboards

[stacey-gammon]

If you have a dashboard created in 6.1 that contains a saved search that has been saved with column or sort overrides on the panel, you will not be able to upgrade to 7.3. (Caveat - this is more theory from looking at the code and knowing the problem than actually tested, but I'm relatively confident).

The issue is, in migrate610PanelToLatest:

  const embeddableConfig = uiState ? uiState[`P-${panel.panelIndex}`] : {};

  // 2. (6.4) remove columns, sort properties
  if (panel.columns || panel.sort) {
    embeddableConfig.columns = panel.columns;
    embeddableConfig.sort = panel.sort;
  }

When uiState is an empty object, embeddableConfig is undefined.

Luckily, the (almost) same code in migratePre61PanelToLatest doesn't have this issue:

  const embeddableConfig = uiState ? uiState[`P-${panel.panelIndex}`] || {} : {};

  if (panel.columns || panel.sort) {
    embeddableConfig.columns = panel.columns;
    embeddableConfig.sort = panel.sort;
  }

so it's only explicitly for 6.1.

Another good point to mention is that this is the start of the bug, but what really kills it is because the document doesn't get updated by the uiStateJSON being removed because it bails early, and the mappings were changed. I could have waited till a major to update the mapping to be more careful.

cc @rudolf @timroes

JSON that will hit the error if imported (created from 6.1)

  {
    "_id": "18bb2490-b536-11e9-b1af-cff0dd87ed28",
    "_type": "dashboard",
    "_source": {
      "title": "dash with overrides",
      "hits": 0,
      "description": "",
      "panelsJSON": "[{\"gridData\":{\"h\":3,\"i\":\"1\",\"w\":6,\"x\":0,\"y\":0},\"id\":\"088bc570-b536-11e9-b1af-cff0dd87ed28\",\"panelIndex\":\"1\",\"type\":\"visualization\",\"version\":\"6.1.4\"},{\"gridData\":{\"w\":6,\"h\":3,\"x\":6,\"y\":0,\"i\":\"2\"},\"version\":\"6.1.4\",\"panelIndex\":\"2\",\"type\":\"search\",\"id\":\"fc91ab90-b535-11e9-b1af-cff0dd87ed28\",\"columns\":[\"_id\",\"_score\",\"status\"],\"sort\":[\"_id\",\"asc\"]}]",
      "optionsJSON": "{\"darkTheme\":false,\"hidePanelTitles\":false,\"useMargins\":true}",
      "uiStateJSON": "{}",
      "version": 1,
      "timeRestore": true,
      "timeTo": "now",
      "timeFrom": "now-15y",
      "refreshInterval": {
        "display": "Off",
        "pause": false,
        "value": 0
      },
      "kibanaSavedObjectMeta": {
        "searchSourceJSON": "{\"query\":{\"language\":\"lucene\",\"query\":\"\"},\"filter\":[],\"highlightAll\":true,\"version\":true}"
      }
    },
    "_meta": {
      "savedObjectVersion": 2
    }
  },