As we discussed in support ticket #1147276 the solution for the issue would be as following:
"To set all values as the default value of multivalue parameter, you can use built-in aggregate functions. The first one is AllValues(Expression, IncludeNullValues))
which returns an array of all values and the second is AllDistinctValues(Expression, IncludeNullValues))
which returns all distinct values from the specified expression.
For more detailed description of the functions, please refer to Aggregate Functions
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