"e.map is not a function" error on time series

Since upgrading to 0.17.5, and now on 0.17.6 alpha1, I get “TypeError: e.map is not a function” in the dev console when trying to generate a line series.

• I have checked the superset logs for python stacktraces and included it here as text if any
• I have reproduced the issue with at least the latest released version of superset
• I have checked the issue tracker for the same issue and I haven’t found one similar

Superset version

0.17.5 and 0.17.6 alpha 1

Expected results

Time series chart renders

Actual results

An empty viz area and this stacktrace in the dev console. Unfortunately the JS is minified.

explorev2.0.17.6-alpha.1.entry.js:144 Uncaught TypeError: e.map is not a function
    at explorev2.0.17.6-alpha.1.entry.js:144
    at r.utils.state.a (explorev2.0.17.6-alpha.1.entry.js:144)
    at r.utils.state.update (explorev2.0.17.6-alpha.1.entry.js:144)
    at SVGSVGElement.<anonymous> (explorev2.0.17.6-alpha.1.entry.js:144)
    at explorev2.0.17.6-alpha.1.entry.js:34
    at $ (explorev2.0.17.6-alpha.1.entry.js:34)
    at Array.ql.each (explorev2.0.17.6-alpha.1.entry.js:34)
    at Array.e (explorev2.0.17.6-alpha.1.entry.js:144)
    at Array.Oa.call (explorev2.0.17.6-alpha.1.entry.js:34)
    at Object.b [as generate] (explorev2.0.17.6-alpha.1.entry.js:39)

Steps to reproduce

Try to create a time series chart in recent versions of Firefox or Chromium/Chrome using 0.17.5 or 0.17.6 alpha1

Note- it looks like e.map is defined just a bit earlier as seen in the screenshots here.

[williamdrake]

I’m getting this issue when trying to load graphs from the Explore function from SQL Lab.

[christophlingg]

when I refresh the page, the js error is gone