Add isset an multiple_dropdown_action

[Lainow]

Checklist before requesting a review

Please delete options that are not relevant.

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• I have updated the CHANGELOG with a short functional description of the fix or new feature.
• This change requires a documentation update.

Description

• It fixes
• Here is a brief description of what this PR does

When importing with DataInjection, for example, an error occurs: Undefined array key ‘multiple_dropdown_action’

Screenshots (if appropriate):