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singleOrNull

fun <T> Sequence<T>.singleOrNull(): T?

Returns single element, or null if the sequence is empty or has more than one element.

inline fun <T> Sequence<T>.singleOrNull(
    predicate: (T) -> Boolean
): T?

Returns the single element matching the given predicate, or null if element was not found or more than one element was found.

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Licensed under the Apache License, Version 2.0.
https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.sequences/single-or-null.html