Handle custom properties in VNS

Throw an exception if VehicleNetwork#getProperty(int) called for custom
property because data type is undefined.

Bug:26729379
Change-Id: I78de2e1059d5c275e828c6ff4b41d4424c7feb6f
diff --git a/tests/libvehiclenetwork-java-test/src/com/android/car/vehiclenetwork/libtest/VehicleNetworkMockedTest.java b/tests/libvehiclenetwork-java-test/src/com/android/car/vehiclenetwork/libtest/VehicleNetworkMockedTest.java
index 956bc65..7b3c5e6 100644
--- a/tests/libvehiclenetwork-java-test/src/com/android/car/vehiclenetwork/libtest/VehicleNetworkMockedTest.java
+++ b/tests/libvehiclenetwork-java-test/src/com/android/car/vehiclenetwork/libtest/VehicleNetworkMockedTest.java
@@ -336,6 +336,15 @@
         mVehicleNetwork.unsubscribe(PROPERTY);
     }
 
+    public void testGetPropertyFailsForCustom() {
+        try {
+            mVehicleNetwork.getProperty(CUSTOM_PROPERTY_INT32);
+            fail();
+        } catch (IllegalArgumentException expected) {
+            // Expected.
+        }
+    }
+
     private void assertArrayEquals(int[] expected, int[] actual) {
         assertEquals(Arrays.toString(expected), Arrays.toString(actual));
     }