NIFI-4948 - MongoDB Lookup Service throws an exception if there is no match

Signed-off-by: Matthew Burgess <mattyb149@apache.org>

This closes #2522

nifi-nar-bundles/nifi-standard-services/nifi-mongodb-services-bundle/nifi-mongodb-services/src/main/java/org/apache/nifi/mongodb/MongoDBControllerService.java

@@ -22,6 +22,7 @@ import com.mongodb.client.MongoCollection;
 import com.mongodb.client.MongoCursor;
 import com.mongodb.client.MongoDatabase;
 import com.mongodb.client.model.UpdateOptions;
+
 import org.apache.nifi.annotation.documentation.CapabilityDescription;
 import org.apache.nifi.annotation.documentation.Tags;
 import org.apache.nifi.annotation.lifecycle.OnDisabled;
@@ -69,9 +70,10 @@ public class MongoDBControllerService extends AbstractMongoDBControllerService i
         return this.col.count(query) > 0;
     }
 
+    @Override
     public Document findOne(Document query) {
         MongoCursor<Document> cursor  = this.col.find(query).limit(1).iterator();
-        Document retVal = cursor.next();
+        Document retVal = cursor.tryNext();
         cursor.close();
 
         return retVal;

nifi-nar-bundles/nifi-standard-services/nifi-mongodb-services-bundle/nifi-mongodb-services/src/main/java/org/apache/nifi/mongodb/MongoDBLookupService.java

@@ -32,6 +32,7 @@ import org.apache.nifi.serialization.record.Record;
 import org.apache.nifi.serialization.record.RecordField;
 import org.apache.nifi.serialization.record.RecordFieldType;
 import org.apache.nifi.serialization.record.RecordSchema;
+import org.apache.nifi.util.StringUtils;
 import org.bson.Document;
 
 import java.io.IOException;
@@ -43,7 +44,6 @@ import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
 
-
 @Tags({"mongo", "mongodb", "lookup", "record"})
 @CapabilityDescription(
     "Provides a lookup service based around MongoDB. Each key that is specified \n" +
@@ -86,7 +86,9 @@ public class MongoDBLookupService extends MongoDBControllerService implements Lo
         try {
             Document result = this.findOne(query);
 
-            if (lookupValueField != null && !lookupValueField.equals("")) {
+            if(result == null) {
+                return Optional.empty();
+            } else if (!StringUtils.isEmpty(lookupValueField)) {
                 return Optional.ofNullable(result.get(lookupValueField));
             } else {
                 final List<RecordField> fields = new ArrayList<>();
@@ -107,6 +109,7 @@ public class MongoDBLookupService extends MongoDBControllerService implements Lo
         }
     }
 
+    @Override
     @OnEnabled
     public void onEnabled(final ConfigurationContext context) throws InitializationException, IOException, InterruptedException {
         this.lookupValueField = context.getProperty(LOOKUP_VALUE_FIELD).getValue();
@@ -125,7 +128,6 @@ public class MongoDBLookupService extends MongoDBControllerService implements Lo
 
     @Override
     protected List<PropertyDescriptor> getSupportedPropertyDescriptors() {
-
         return lookupDescriptors;
     }
 }

nifi-nar-bundles/nifi-standard-services/nifi-mongodb-services-bundle/nifi-mongodb-services/src/test/java/org/apache/nifi/mongodb/TestMongoDBLookupService.java

@@ -82,14 +82,13 @@ public class TestMongoDBLookupService {
         clean.putAll(criteria);
         service.delete(new Document(clean));
 
-        boolean error = false;
         try {
-            service.lookup(criteria);
+            result = service.lookup(criteria);
         } catch (LookupFailureException ex) {
-            error = true;
+            Assert.fail();
         }
 
-        Assert.assertTrue("An error should have been thrown.", error);
+        Assert.assertTrue(!result.isPresent());
     }
 
     @Test
@@ -113,14 +112,13 @@ public class TestMongoDBLookupService {
         clean.putAll(criteria);
         service.delete(new Document(clean));
 
-        boolean error = false;
         try {
-            service.lookup(criteria);
+            result = service.lookup(criteria);
         } catch (LookupFailureException ex) {
-            error = true;
+            Assert.fail();
         }
 
-        Assert.assertTrue("An error should have been thrown.", error);
+        Assert.assertTrue(!result.isPresent());
     }
 
     @Test