Remove squared brackets in Alerts Composer notifications

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We have a problem regarding editting expressions in the Alerts Composer. 

In the e-Mails, which are sent through Alerts Composer, there are always displayed "squared brackets"[ ] around the text.

Previously the brackets were not displayed, if we inserted "[0]" in the expression: ${learnerLearningRecords [0] .otherSelectedCourseOfferings.requestedDate}
But now we get an error message, when we insert "[0]" and the mail isn't sent.

Does anybody know how to change the expression in order to remove the brackets?

 

Thanks an advance