BouncerKeyguardMessage doesn't always get cleared when being set to null.

Hypothesis: textAboutToShow == msg check can potentially skip such invocations.

Bug: 249475000
Test: atest BouncerKeyguardMessageAreaTest

Change-Id: I5d198c0e693fd96c9ad5d5528452206bf871eccc

packages/SystemUI/src/com/android/keyguard/BouncerKeyguardMessageArea.kt

@@ -70,7 +70,7 @@ open class BouncerKeyguardMessageArea(context: Context?, attrs: AttributeSet?) :
     }
 
     override fun setMessage(msg: CharSequence?) {
-        if (msg == textAboutToShow || msg == text) {
+        if ((msg == textAboutToShow && msg != null) || msg == text) {
             return
         }
         textAboutToShow = msg

packages/SystemUI/tests/src/com/android/keyguard/BouncerKeyguardMessageAreaTest.kt

@@ -66,4 +66,13 @@ class BouncerKeyguardMessageAreaTest : SysuiTestCase() {
         underTest.setMessage(null)
         assertThat(underTest.text).isEqualTo("")
     }
+
+    @Test
+    fun testSetNullClearsPreviousMessage() {
+        underTest.setMessage("something not null")
+        assertThat(underTest.text).isEqualTo("something not null")
+
+        underTest.setMessage(null)
+        assertThat(underTest.text).isEqualTo("")
+    }
 }