Filter out empty phone number

Prevent flicker.

Bug: 318310357
Test: manual - on SIMs
Test: unit test
Change-Id: Ie44ec8bad58b59368099d0fe3f277c12855f8bd4

tests/spa_unit/src/com/android/settings/network/telephony/SubscriptionRepositoryTest.kt

@@ -141,10 +141,27 @@ class SubscriptionRepositoryTest {
         assertThat(subInfos.map { it.subscriptionId }).containsExactly(SUB_ID_1)
     }
 
+    @Test
+    fun phoneNumberFlow() = runBlocking {
+        mockSubscriptionManager.stub {
+            on { getPhoneNumber(SUB_ID_1) } doReturn NUMBER_1
+        }
+        val subInfo = SubscriptionInfo.Builder().apply {
+            setId(SUB_ID_1)
+            setMcc(MCC)
+        }.build()
+
+        val phoneNumber = context.phoneNumberFlow(subInfo).firstWithTimeoutOrNull()
+
+        assertThat(phoneNumber).isEqualTo(NUMBER_1)
+    }
+
     private companion object {
         const val SUB_ID_1 = 1
         const val SUB_ID_2 = 2
         val GROUP_UUID = UUID.randomUUID().toString()
         const val SIM_SLOT_INDEX = 1
+        const val NUMBER_1 = "000000001"
+        const val MCC = "310"
     }
 }