kotlin-stdlib / kotlin.sequences / singleOrNull singleOrNull fun <T> Sequence<T>.singleOrNull(): T? (source) Returns single element, or null if the sequence is empty or has more than one element. The operation is terminal. inline fun <T> Sequence<T>.singleOrNull( predicate: (T) -> Boolean): T? (source) Returns the single element matching the given predicate, or null if element was not found or more than one element was found. The operation is terminal.