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

#KT-9188

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))
     }