Throw CelAttributeNotFoundException in ProtoMessageLiteValue.find for undeclared fields

common/src/main/java/dev/cel/common/values/ProtoMessageLiteValue.java

@@ -133,19 +133,23 @@ public final String toString() {
 
   @Override
   public Object select(String field) {
-    FieldLiteDescriptor fd = descriptor().findByFieldName(field);
-    if (fd == null) {
-      throw CelAttributeNotFoundException.of(
-          String.format("field '%s' is not declared in message '%s'", field, protoTypeName()));
-    }
+    FieldLiteDescriptor fd = findFieldDescriptor(field);
     Object fieldValue = readField(fd);
     return fieldValue != null ? fieldValue : protoLiteCelValueConverter().getDefaultCelValue(fd);
   }
 
   @Override
   public Optional<Object> find(String field) {
-    // Per SelectableValue#find, a field that doesn't exist is reported as absent.
-    return Optional.ofNullable(descriptor().findByFieldName(field)).map(this::readField);
+    return Optional.ofNullable(readField(findFieldDescriptor(field)));
+  }
+
+  private FieldLiteDescriptor findFieldDescriptor(String field) {
+    FieldLiteDescriptor fd = descriptor().findByFieldName(field);
+    if (fd == null) {
+      throw CelAttributeNotFoundException.of(
+          String.format("field '%s' is not declared in message '%s'", field, protoTypeName()));
+    }
+    return fd;
   }
 
   @Override

common/src/test/java/dev/cel/common/values/ProtoMessageLiteValueTest.java

@@ -368,32 +368,35 @@ public void select_undeclaredField_throwsCelAttributeNotFoundException() {
                 + " 'cel.expr.conformance.proto3.TestAllTypes'");
   }
 
-  @SuppressWarnings("ImmutableEnumChecker") // Test only
-  private enum FindFieldTestCase {
-    PRESENT("single_string", Optional.of("foo")),
-    ABSENT("single_int64", Optional.empty()),
-    UNDECLARED("undeclared_field", Optional.empty());
+  @Test
+  public void find_undeclaredField_throwsCelAttributeNotFoundException() {
+    ProtoMessageLiteValue messageLiteValue =
+        ProtoMessageLiteValue.create(
+            TestAllTypes.getDefaultInstance(),
+            TEST_ALL_TYPES_DESCRIPTOR,
+            PROTO_LITE_CEL_VALUE_CONVERTER);
 
-    private final String fieldName;
-    private final Optional<Object> expected;
+    CelAttributeNotFoundException thrown =
+        assertThrows(
+            CelAttributeNotFoundException.class, () -> messageLiteValue.find("undeclared_field"));
 
-    FindFieldTestCase(String fieldName, Optional<Object> expected) {
-      this.fieldName = fieldName;
-      this.expected = expected;
-    }
+    assertThat(thrown)
+        .hasMessageThat()
+        .isEqualTo(
+            "field 'undeclared_field' is not declared in message"
+                + " 'cel.expr.conformance.proto3.TestAllTypes'");
   }
 
   @Test
-  public void find_returnsValueOnlyIfFieldIsPresent(@TestParameter FindFieldTestCase testCase) {
+  public void find_returnsValueOnlyIfFieldIsPresent() {
     ProtoMessageLiteValue messageLiteValue =
         ProtoMessageLiteValue.create(
             TestAllTypes.newBuilder().setSingleString("foo").build(),
             TEST_ALL_TYPES_DESCRIPTOR,
             PROTO_LITE_CEL_VALUE_CONVERTER);
 
-    Optional<Object> result = messageLiteValue.find(testCase.fieldName);
-
-    assertThat(result).isEqualTo(testCase.expected);
+    assertThat(messageLiteValue.find("single_string")).hasValue("foo");
+    assertThat(messageLiteValue.find("single_int64")).isEmpty();
   }
 
   @SuppressWarnings("ImmutableEnumChecker") // Test only