Pasting table into table adds spaces in empty cells

[FilipTokarski]

📝 Provide detailed reproduction steps (if any)

1. Go to demo
2. Paste some table into another one, both empty
   To see the result more clearly, create a big selection and add a background color.

✔️ Expected result

Pasted cells are empty, there are no spaces added

❌ Actual result

Single spaces are added in pasted cells:

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[jodator]

Let's take a quick look at it - it might be wrong handling of   handling. DomConverter of something might have there wrong block filler mode set.