Sort function is guessed as sortAlpha and cached when sort applied to empty grid

When there is no data in the grid and the user clicks to sort a column, the row sort function will be cached based on the guess (sortAlpha). Say this is a numeric column and you later add data, it will always sort as alpha because the guess was cached.

Workaround (and probably best practice): specify explicitly rather than rely on guess. But it's possible to accidentally rely on guess.

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