Add Collections.isNullOrEmpty #KT-23279

libraries/stdlib/samples/test/samples/collections/collections.kt

@@ -51,6 +51,18 @@ class Collections {
             assertPrints(collection.orEmpty(), "[a, b, c]")
         }
 
+        @Sample
+        fun collectionIsNullOrEmpty() {
+            val nullCollection: Collection<Any>? = null
+            assertTrue(nullCollection.isNullOrEmpty())
+
+            val emptyCollection: Collection<Any>? = listOf()
+            assertTrue(emptyCollection.isNullOrEmpty())
+
+            val collection: Collection<Char>? = listOf('a', 'b', 'c')
+            assertFalse(collection.isNullOrEmpty())
+        }
+
         @Sample
         fun collectionContainsAll() {
             val collection = mutableListOf('a', 'b')

libraries/stdlib/src/kotlin/collections/Collections.kt

@@ -10,6 +10,7 @@ package kotlin.collections
 
 import kotlin.*
 import kotlin.comparisons.compareValues
+import kotlin.internal.contracts.*
 
 internal object EmptyIterator : ListIterator<Nothing> {
     override fun hasNext(): Boolean = false
@@ -168,6 +169,19 @@ public val <T> List<T>.lastIndex: Int
 @kotlin.internal.InlineOnly
 public inline fun <T> Collection<T>.isNotEmpty(): Boolean = !isEmpty()
 
+/**
+ * Returns `true` if the collection is null or if it is empty.
+ * @sample samples.collections.Collections.Collections.collectionIsNullOrEmpty
+ */
+@kotlin.internal.InlineOnly
+public inline fun <T> Collection<T>?.isNullOrEmpty(): Boolean {
+    contract {
+        returns(false) implies (this@isNullOrEmpty != null)
+    }
+
+    return this == null || this.isEmpty()
+}
+
 /**
  * Returns this Collection if it's not `null` and the empty list otherwise.
  * @sample samples.collections.Collections.Collections.collectionOrEmpty