Numeric calculation in "Merge selected features" dialog does not work

[qgib]

Author Name: Harrissou Santanna (@DelazJ)
Original Redmine Issue: 20142
Affected QGIS version: 3.3(master)
Redmine category:editing

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Select two features and click on "merge selected features" button
In the new dialog, for a numeric field try to use statistics functions like sum, count or whatever. The field in the "Merge" row becomes empty. If you try some statistics on a literal field you get the result in the field.
It's not simply a display issue given that if you do the merge, you get 0 in the numeric field.
I check "data corruption" as this is a tool that applies in-place modification and gives a wrong value you can not easily check later on/or rebuild.

[qgib]

Author Name: Giovanni Manghi (@gioman)

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Please try on QGIS 3.4.1, if the issue is still valid change the affected version, thanks.

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• status_id was changed from Open to Feedback

[qgib]

Author Name: Nyall Dawson (@nyalldawson)

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This works fine here. You'll need to post more detailed steps to reproduce.

[qgib]

Author Name: Harrissou Santanna (@DelazJ)

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can't reproduce anymore.

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• resolution was changed from to worksforme
• status_id was changed from Feedback to Closed