The () block is a reporter block and an operators block that sends the string you input into it. As it seems useless, it is useful for inputs that do not support text (such as set costume and other dropdowns). The default value for this block is "foo".

()
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Caption
Block Type Reporter
Category / Extension Operators
Status
This article is about the block in the operators category. For other uses, see () (disambiguation).

Workaround

This block can be replicated by using any reporter that outputs the wanted string (ex. join () (text)):

join [] [text] //the first input is empty