Remove the type constraint for Flow.singleOrNull

Author: ansman

kotlinx-coroutines-core/common/src/flow/terminal/Reduce.kt

@@ -71,7 +71,7 @@ public suspend fun <T> Flow<T>.single(): T {
  * The terminal operator, that awaits for one and only one value to be published.
  * Throws [IllegalStateException] for flow that contains more than one element.
  */
-public suspend fun <T: Any> Flow<T>.singleOrNull(): T? {
+public suspend fun <T> Flow<T>.singleOrNull(): T? {
     var result: T? = null
     collect { value ->
         if (result != null) error("Expected only one element")

kotlinx-coroutines-core/common/test/flow/terminal/SingleTest.kt

@@ -61,6 +61,10 @@ class SingleTest : TestBase() {
         assertEquals(1, flowOf<Int?>(1).single())
         assertNull(flowOf<Int?>(null).single())
         assertFailsWith<NoSuchElementException> { flowOf<Int?>().single() }
+
+        assertEquals(1, flowOf<Int?>(1).singleOrNull())
+        assertNull(flowOf<Int?>(null).singleOrNull())
+        assertFailsWith<NoSuchElementException> { flowOf<Int?>().singleOrNull() }
     }
 
     @Test