Allow equals with ignoreCase parameter to take nullable Strings both as a receiver and a parameter.

#KT-9188

js/js.libraries/src/core/stringsCode.kt

@@ -47,11 +47,13 @@ public inline fun CharSequence.isEmpty(): Boolean = this.length() == 0
 
 public fun String.isBlank(): Boolean = length() == 0 || matches("^[\\s\\xA0]+$")
 
-public fun String.equals(anotherString: String, ignoreCase: Boolean = false): Boolean =
-        if (!ignoreCase)
+public fun String?.equals(anotherString: String?, ignoreCase: Boolean = false): Boolean =
+        if (this == null)
+            anotherString == null
+        else if (!ignoreCase)
             this == anotherString
         else
-            this.toLowerCase() == anotherString.toLowerCase()
+            anotherString != null && this.toLowerCase() == anotherString.toLowerCase()
 
 
 public fun String.regionMatches(thisOffset: Int, other: String, otherOffset: Int, length: Int, ignoreCase: Boolean = false): Boolean {

libraries/stdlib/src/kotlin/text/StringsJVM.kt

@@ -34,7 +34,9 @@ internal fun String.nativeLastIndexOf(str: String, fromIndex: Int): Int = (this
  *
  * @param ignoreCase `true` to ignore character case when comparing strings. By default `false`.
  */
-public fun String.equals(anotherString: String, ignoreCase: Boolean = false): Boolean {
+public fun String?.equals(anotherString: String?, ignoreCase: Boolean = false): Boolean {
+    if (this === null)
+        return anotherString === null
     return if (!ignoreCase)
         (this as java.lang.String).equals(anotherString)
     else

libraries/stdlib/test/text/StringTest.kt

@@ -528,6 +528,10 @@ class StringTest {
     @test fun equalsIgnoreCase() {
         assertFalse("sample".equals("Sample", ignoreCase = false))
         assertTrue("sample".equals("Sample", ignoreCase = true))
+        assertFalse("sample".equals(null, ignoreCase = false))
+        assertFalse("sample".equals(null, ignoreCase = true))
+        assertTrue(null.equals(null, ignoreCase = true))
+        assertTrue(null.equals(null, ignoreCase = false))
     }