[Settings] Avoid from crash - SystemProp default null

Default system properties should not have "null" as default value.

Bug: 177843016
Change-Id: Idc2b3aaafd1094ba3fbfa859c4ad7a597e1b7a99
Test: build pass
(cherry picked from commit d2eda630e2dc42ca4efdb0a45702de8452dd78c7)
diff --git a/src/com/android/settings/network/telephony/MobileNetworkUtils.java b/src/com/android/settings/network/telephony/MobileNetworkUtils.java
index 6e5d4b7..bad650d 100644
--- a/src/com/android/settings/network/telephony/MobileNetworkUtils.java
+++ b/src/com/android/settings/network/telephony/MobileNetworkUtils.java
@@ -279,7 +279,7 @@
         final ContentResolver cr = context.getContentResolver();
         final boolean esimIgnoredDevice =
                 Arrays.asList(TextUtils.split(SystemProperties.get(KEY_ESIM_CID_IGNORE, ""), ","))
-                        .contains(SystemProperties.get(KEY_CID, null));
+                        .contains(SystemProperties.get(KEY_CID));
         final boolean enabledEsimUiByDefault =
                 SystemProperties.getBoolean(KEY_ENABLE_ESIM_UI_BY_DEFAULT, true);
         final boolean euiccProvisioned =