Refactor fields: an expression is always required (otherwise python error is thrown)

[qgib]

Author Name: Paolo Cavallini (@pcav)
Original Redmine Issue: 15640
Affected QGIS version: 3.0.0
Redmine category:processing/core

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When creating a new field through Processing > Refactor fields, an expression seems always required. I do not think this should be necessary, because users sometimes want just to add a new empty column to be filled afterwards.

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• easy_fix was configured as 0
• regression was configured as 0

[qgib]

Author Name: Paolo Cavallini (@pcav)

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Adding a string whatsoever is a workaround, but I still think the alg should accept an empty expression instead of throwing:

Traceback (most recent call last): File "/usr/local/src/qgis/QGIS/build_qgis3/output/python/plugins/processing/algs/qgis/FieldsMapper.py", line 144, in prepareAlgorithm expression.parserErrorString())) _core.QgsProcessingException: Parser error in expression "": syntax error, unexpected $end

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• assigned_to_id removed Victor Olaya
• version was changed from 2.16.3 to 3.0.0

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• subject was changed from Refactor fields: an expression is always required to Refactor fields: an expression is always required (otherwise python error is thrown)
• category_id was changed from Processing/GUI to Processing/Core

[qgib]

Author Name: Nyall Dawson (@nyalldawson)

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Applied in changeset cc10bbd.

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• status_id was changed from Open to Closed
• done_ratio was changed from 0 to 100

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• resolution was changed from to fixed/implemented