diff --git a/libraries/stdlib/src/kotlin/Lists.kt b/libraries/stdlib/src/kotlin/Lists.kt
index e9db3773177..8c4c0dabac1 100644
--- a/libraries/stdlib/src/kotlin/Lists.kt
+++ b/libraries/stdlib/src/kotlin/Lists.kt
@@ -67,3 +67,16 @@ public inline fun <T> List<T>.reduceRight(operation: (T, T) -> T) : T {
 
     return r
 }
+
+/**
+ * Returns a original Iterable containing all the non-*null* elements, throwing an [[IllegalArgumentException]] if there are any null elements
+ */
+public inline fun <T:Any> List<T?>.requireNoNulls() : List<T> {
+    for (element in this) {
+        if (element == null) {
+            throw IllegalArgumentException("null element found in $this")
+        }
+    }
+    return this as List<T>
+}
+
diff --git a/libraries/tools/kdoc/src/main/kotlin/org/jetbrains/kotlin/doc/KDocConfig.kt b/libraries/tools/kdoc/src/main/kotlin/org/jetbrains/kotlin/doc/KDocConfig.kt
index 21722f99a0d..eebe743f7a9 100644
--- a/libraries/tools/kdoc/src/main/kotlin/org/jetbrains/kotlin/doc/KDocConfig.kt
+++ b/libraries/tools/kdoc/src/main/kotlin/org/jetbrains/kotlin/doc/KDocConfig.kt
@@ -1,7 +1,6 @@
 package org.jetbrains.kotlin.doc
 
 import java.util.*
-import org.jetbrains.kotlin.doc.model.KPackage
 
 /**
 * The configuration used with KDoc
@@ -114,7 +113,7 @@ class KDocConfig() {
 
 private class LongestFirstStringComparator() : Comparator<String> {
     public override fun compare(s1: String, s2: String): Int {
-        return compareBy(s1, s2, { length() }, { this })
+        return compareBy<String>(s1, s2, { length() }, { this })
     }
 
     public override fun equals(obj : Any?) : Boolean {
diff --git a/libraries/tools/kdoc/src/main/kotlin/org/jetbrains/kotlin/doc/model/KModelCompilerPlugin.kt b/libraries/tools/kdoc/src/main/kotlin/org/jetbrains/kotlin/doc/model/KModelCompilerPlugin.kt
index 840518bba46..a8b91d4c1b6 100644
--- a/libraries/tools/kdoc/src/main/kotlin/org/jetbrains/kotlin/doc/model/KModelCompilerPlugin.kt
+++ b/libraries/tools/kdoc/src/main/kotlin/org/jetbrains/kotlin/doc/model/KModelCompilerPlugin.kt
@@ -3,7 +3,6 @@ package org.jetbrains.kotlin.doc.model
 import java.io.File
 import org.jetbrains.jet.cli.common.CompilerPlugin
 import org.jetbrains.jet.cli.common.CompilerPluginContext
-import org.jetbrains.kotlin.doc.KDocArguments
 
 /** Base class for any compiler plugin which needs to process a KModel */
 abstract class KModelCompilerPlugin(
@@ -17,7 +16,7 @@ abstract class KModelCompilerPlugin(
         val bindingContext = context.getContext()
         val sources = context.getFiles()
         val sourceDirs: List<File> = arguments.getSourceDirs().orEmpty().requireNoNulls().map { path -> File(path) }
-        val model = KModel(bindingContext, arguments.apply(), sourceDirs, sources.orEmpty().requireNoNulls())
+        val model = KModel(bindingContext, arguments.apply(), sourceDirs, sources.requireNoNulls())
 
         processModel(model)
     }