Resolve comments

Author: Yufei Gu

polaris-core/src/test/java/org/apache/polaris/core/policy/PolicyTypeTest.java

@@ -20,10 +20,13 @@
 
 import java.util.stream.Stream;
 import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.MethodSource;
 
+import static org.assertj.core.api.Assertions.assertThat;
+
 public class PolicyTypeTest {
 
   static Stream<Arguments> predefinedPolicyTypes() {
@@ -53,4 +56,14 @@ public void testPredefinedPolicyTypeFromName(int code, String name, boolean isIn
     Assertions.assertThat(policyType.getName()).isEqualTo(name);
     Assertions.assertThat(policyType.isInheritable()).isEqualTo(isInheritable);
   }
+
+  @Test
+  void fromCodeReturnsNullForNegative() {
+    assertThat(PolicyType.fromCode(-1)).isNull();
+  }
+
+  @Test
+  void fromNameReturnsNullForUnknown() {
+    assertThat(PolicyType.fromName("__unknown__")).isNull();
+  }
 }