Custom functoid with Array/List?

Would it be possible to make the functoid to return Array/List? I tried, no luck so far.
I am getting the following error.

XSL transform error: Unable to write output instance to the following
Object of type ‘System.String’ cannot be converted to type ‘System.Collections.Generic.List`1[System.Object[]]’.

Here, I use custom functoid as input for script functoid.
I wrote the functoid to return the List of String array. So my script functoid expection list of string array type. It looks like custom functoid is returning string.
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Thank you,

Siva