Fill missing time intervals with zero

[DL6ER]

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• I have read and understood the contributors guide, as well as this entire template.
• I have made only one major change in my proposed changes.
• I have commented my proposed changes within the code.
• I have tested my proposed changes, and have included unit tests where possible.
• I am willing to help maintain this change if there are issues with it later.
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• It is compatible with the EUPL 1.2 license
• I have squashed any insignificant commits. (git rebase)

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What does this PR aim to accomplish?:

Fix #1211

How does this PR accomplish the above?:

Fill empty slots with aligned zeros.

What documentation changes (if any) are needed to support this PR?:

None