Minor. Utility moved to a common place

core/util.runtime/src/org/jetbrains/jet/utils/collections.kt

@@ -80,3 +80,7 @@ public fun <T> Iterable<Iterable<T>>.flatten(): List<T> {
 }
 
 public fun <T: Any> emptyOrSingletonList(item: T?): List<T> = if (item == null) listOf() else listOf(item)
+
+public fun <T: Any> MutableCollection<T>.addIfNotNull(t: T?) {
+    if (t != null) add(t)
+}

idea/src/org/jetbrains/jet/plugin/codeInsight/KotlinCopyPasteReferenceProcessor.kt

@@ -371,5 +371,3 @@ private fun PsiElement.isInCopiedArea(fileCopiedFrom: JetFile, startOffsets: Int
         range in TextRange(start, end)
     }
 }
-
-private fun <T : Any> MutableCollection<T>.addIfNotNull(el: T?) = ContainerUtil.addIfNotNull(this, el)