OZG-5899 map empty field to empty list

bescheid-manager/src/main/java/de/ozgcloud/bescheid/BescheidMapper.java

@@ -93,7 +93,7 @@ public interface BescheidMapper {
 	}
 
 	default Optional<List<FileId>> mapToAttachments(Object attachments) {
-		if (Objects.isNull(attachments)) {
+		if (Objects.isNull(attachments) || StringUtils.isEmpty(String.valueOf(attachments))) {
 			return Optional.empty();
 		}
 		if (attachments instanceof Collection<?> attachmentList) {

bescheid-manager/src/test/java/de/ozgcloud/bescheid/BescheidMapperTest.java

@@ -7,6 +7,7 @@ import static org.mockito.Mockito.*;
 import java.util.Collections;
 import java.util.List;
 
+import org.apache.commons.lang3.StringUtils;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Nested;
@@ -99,6 +100,13 @@ class BescheidMapperTest {
 
 			assertThat(attachments).hasValue(Collections.singletonList(BescheidTestFactory.ATTACHMENT));
 		}
+
+		@Test
+		void shouldMapEmptyStringToEmptyList() {
+			var attachments = mapper.mapToAttachments(StringUtils.EMPTY);
+
+			assertThat(attachments).isEmpty();
+		}
 	}
 
 	@DisplayName("To get bescheid draft response")