Fix #616 CommonFileStore: when a user adds a filestore and then tries to delete the filestore the application crashes

[joao4all]

Prerequisites

• [x] I have written a descriptive pull-request title
• [x] I have verified that there are no overlapping pull-requests open
• [x] I have verified that I am following the COMET-WEB code style guidelines
• [x] I have provided test coverage for my change (where applicable)

Description

Closes #616 CommonFileStore: when a user adds a filestore and then tries to delete the filestore the application crashes

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

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