diff --git a/jdk-annotations/java/nio/charset/annotations.xml b/jdk-annotations/java/nio/charset/annotations.xml
index c0b6549d796..68c1fdca219 100644
--- a/jdk-annotations/java/nio/charset/annotations.xml
+++ b/jdk-annotations/java/nio/charset/annotations.xml
@@ -138,5 +138,8 @@
     <item name="java.nio.charset.UnmappableCharacterException java.lang.String getMessage()">
         <annotation name="org.jetbrains.annotations.NotNull"/>
     </item>
+    <item name="java.nio.charset.Charset java.nio.charset.Charset defaultCharset()">
+        <annotation name="org.jetbrains.annotations.NotNull"/>
+    </item>
 </root>
 
diff --git a/libraries/stdlib/src/kotlin/StringsJVM.kt b/libraries/stdlib/src/kotlin/StringsJVM.kt
index 0c28d711abb..75ec8609cce 100644
--- a/libraries/stdlib/src/kotlin/StringsJVM.kt
+++ b/libraries/stdlib/src/kotlin/StringsJVM.kt
@@ -5,6 +5,7 @@ import java.util.ArrayList
 import java.util.HashMap
 import java.util.HashSet
 import java.util.LinkedList
+import java.nio.charset.Charset
 
 public inline fun String.lastIndexOf(str: String) : Int = (this as java.lang.String).lastIndexOf(str)
 
@@ -62,11 +63,11 @@ public inline fun String.endsWith(ch: Char) : Boolean = (this as java.lang.Strin
 
 public inline fun String(bytes : ByteArray, offset : Int, length : Int, charsetName : String) : String = java.lang.String(bytes, offset, length, charsetName) as String
 
-public inline fun String(bytes : ByteArray, offset : Int, length : Int, charset : java.nio.charset.Charset) : String = java.lang.String(bytes, offset, length, charset) as String
+public inline fun String(bytes : ByteArray, offset : Int, length : Int, charset : Charset) : String = java.lang.String(bytes, offset, length, charset) as String
 
 public inline fun String(bytes : ByteArray, charsetName : String) : String = java.lang.String(bytes, charsetName) as String
 
-public inline fun String(bytes : ByteArray, charset : java.nio.charset.Charset) : String = java.lang.String(bytes, charset) as String
+public inline fun String(bytes : ByteArray, charset : Charset) : String = java.lang.String(bytes, charset) as String
 
 public inline fun String(bytes : ByteArray, i : Int, i1 : Int) : String = java.lang.String(bytes, i, i1) as String
 
@@ -98,7 +99,7 @@ public inline fun String.contentEquals(cs : CharSequence) : Boolean = (this as j
 
 public inline fun String.contentEquals(sb : StringBuffer) : Boolean = (this as java.lang.String).contentEquals(sb)
 
-public inline fun String.getBytes(charset : java.nio.charset.Charset) : ByteArray = (this as java.lang.String).getBytes(charset)
+public inline fun String.getBytes(charset : Charset) : ByteArray = (this as java.lang.String).getBytes(charset)
 
 public inline fun String.getBytes(charsetName : String) : ByteArray = (this as java.lang.String).getBytes(charsetName)
 
@@ -146,8 +147,8 @@ public inline fun CharSequence.toString() : String? = (this as java.lang.CharSeq
 public inline fun CharSequence.length() : Int = (this as java.lang.CharSequence).length()
 
 
-public inline fun String.toByteArray(encoding: String = java.nio.charset.Charset.defaultCharset()!!.name()):ByteArray = (this as java.lang.String).getBytes(encoding)
-public inline fun String.toByteArray(encoding: java.nio.charset.Charset):ByteArray =  (this as java.lang.String).getBytes(encoding)
+public inline fun String.toByteArray(encoding: String = Charset.defaultCharset().name()): ByteArray = (this as java.lang.String).getBytes(encoding)
+public inline fun String.toByteArray(encoding: Charset): ByteArray =  (this as java.lang.String).getBytes(encoding)
 
 public inline fun String.toBoolean() : Boolean = java.lang.Boolean.parseBoolean(this)
 public inline fun String.toShort() : Short = java.lang.Short.parseShort(this)
diff --git a/libraries/stdlib/src/kotlin/io/Files.kt b/libraries/stdlib/src/kotlin/io/Files.kt
index 3468de7a7a0..1cc10c95aa4 100644
--- a/libraries/stdlib/src/kotlin/io/Files.kt
+++ b/libraries/stdlib/src/kotlin/io/Files.kt
@@ -114,25 +114,25 @@ public fun File.appendBytes(data: ByteArray): Unit {
  *
  * This method is not recommended on huge files.
  */
-public fun File.readText(encoding:String = java.nio.charset.Charset.defaultCharset()!!.name()) : String = readBytes().toString(encoding)
+public fun File.readText(encoding:String = Charset.defaultCharset().name()) : String = readBytes().toString(encoding)
 
 /**
  * Reads the entire content of the file as a String using a character encoding.
  *
  * This method is not recommended on huge files.
  */
-public fun File.readText(encoding:Charset) : String = readBytes().toString(encoding)
+public fun File.readText(encoding: Charset) : String = readBytes().toString(encoding)
 
 /**
  * Writes the text as the contents of the file using the a
  * character encoding.
  */
-public fun File.writeText(text: String, encoding:String = java.nio.charset.Charset.defaultCharset()!!.name()): Unit { writeBytes(text.toByteArray(encoding)) }
+public fun File.writeText(text: String, encoding: String = Charset.defaultCharset().name()): Unit { writeBytes(text.toByteArray(encoding)) }
 
 /**
  * Writes the text as the contents of the file using a character encoding.
  */
-public fun File.writeText(text: String, encoding:Charset): Unit { writeBytes(text.toByteArray(encoding)) }
+public fun File.writeText(text: String, encoding: Charset): Unit { writeBytes(text.toByteArray(encoding)) }
 
 /**
  * Appends text to the contents of the file using a given character encoding.
@@ -144,7 +144,7 @@ public fun File.appendText(text: String, encoding: Charset): Unit {
 /**
  * Appends text to the contents of the file using a character encoding.
  */
-public fun File.appendText(text: String, encoding: String = java.nio.charset.Charset.defaultCharset()!!.name()): Unit {
+public fun File.appendText(text: String, encoding: String = Charset.defaultCharset().name()): Unit {
     appendBytes(text.toByteArray(encoding))
 }
 
diff --git a/libraries/stdlib/src/kotlin/io/JIO.kt b/libraries/stdlib/src/kotlin/io/JIO.kt
index 91eb5c1fc53..d9b87799761 100644
--- a/libraries/stdlib/src/kotlin/io/JIO.kt
+++ b/libraries/stdlib/src/kotlin/io/JIO.kt
@@ -319,7 +319,7 @@ public fun Reader.copyTo(out: Writer, bufferSize: Int = defaultBufferSize): Long
  *
  * This method is not recommended on huge files.
  */
-public fun URL.readText(encoding: String = java.nio.charset.Charset.defaultCharset()!!.name()): String = readBytes().toString(encoding)
+public fun URL.readText(encoding: String = Charset.defaultCharset().name()): String = readBytes().toString(encoding)
 
 /**
  * Reads the entire content of the URL as a String with the specified character encoding.