为什么它在没有找到匹配时返回空值但是返回布尔类型

I am using the following code to search an element inside a multi dimensional array.When a match is found it returns the index.But when no match is found it returns a empty value.Not 0 or 1.But if i print out the type , it says boolean.What does that boolean mean if it returns empty.Does it mean that it will be equal to empty string ?I am using the following code to search an elem