return empty if query is empty

src/main/java/com/danielbohry/stocks/service/StockService.java

@@ -7,6 +7,7 @@ import lombok.extern.slf4j.Slf4j;
 import org.springframework.stereotype.Service;
 
 import java.util.List;
+import java.util.Objects;
 
 import static java.util.Collections.emptyList;
 
@@ -18,7 +19,7 @@ public class StockService {
     private StockRepository repository;
 
     public List<Quote> get(String query) {
-        if (query == null) {
+        if (Objects.equals(query, "")) {
             return emptyList();
         }