Fix blank map when loading widgets for tilesets

[Shylpx]

Description

With this change now data can be null, so this breaks some widgets (like CategoryWidget, or HistogramWidget), when they access to the .length propertly.

In the past, we were ignoring undefined and null values, and undefined works fine because a default empty array is used. However, for null values, the map crashes. I was able to reproduce it with tilesets using category and histogram widgets, when we are dropping features.

Type of change

• Fix

Acceptance

• Without the change

• With the change (local environment)

[shortcut-integration]

This pull request has been linked to Shortcut Story #327815: [team] Blank map when loading a widget from a tileset table.

[github-actions]

Pull Request Test Coverage Report for Build 5466430457

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.009%) to 71.625%

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Totals
Change from base Build 5462921253:	-0.009%
Covered Lines:	2256
Relevant Lines:	2920

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💛 - Coveralls

[github-actions]

Visit the preview URL for this PR (updated for commit 69d8834):

https://cartodb-fb-storybook-react-dev--pr733-bug-sc-327815-te-c6kcoe5v.web.app

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