Introduce T.addTo(MutableCollection<T>)
#KT-5166 Fixed

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

diff --git a/libraries/stdlib/src/kotlin/collections/MutableCollections.kt b/libraries/stdlib/src/kotlin/collections/MutableCollections.kt
index e2ceb07..2a46cbb 100644
--- a/libraries/stdlib/src/kotlin/collections/MutableCollections.kt
+++ b/libraries/stdlib/src/kotlin/collections/MutableCollections.kt
@@ -136,6 +136,15 @@
 public fun <K, V> MutableMap<K, V>.values(): MutableCollection<V> = values
 
 /**
+ * Adds this object to the specified [collection].
+ *
+ * Can be used with safe call: `nullableValue?.addTo(collectionOfNonNullables)`.
+ */
+public fun <T> T.addTo(collection: MutableCollection<in T>) {
+    collection.add(this)
+}
+
+/**
  * Adds the specified [element] to this mutable collection.
  */
 public operator fun <T> MutableCollection<in T>.plusAssign(element: T) {