ServletTest#buildJsonRaw: Annotate queryString parameter as @Nullable

The queryString parameter may be null, but dereferencing it is
protected by a call to Strings.isNullOrEmpty.

Change-Id: I2c9a0a7dbd04719b5ad3c64016e585a8409574fe

javatests/com/google/gitiles/ServletTest.java

diff --git a/javatests/com/google/gitiles/ServletTest.java b/javatests/com/google/gitiles/ServletTest.java
index 5c1eea1..c642a79 100644
--- a/javatests/com/google/gitiles/ServletTest.java
+++ b/javatests/com/google/gitiles/ServletTest.java
@@ -27,6 +27,7 @@
 import com.google.gson.reflect.TypeToken;
 import java.util.Map;
 import java.util.Optional;
+import javax.annotation.Nullable;
 import org.eclipse.jgit.internal.storage.dfs.DfsRepository;
 import org.eclipse.jgit.internal.storage.dfs.DfsRepositoryDescription;
 import org.eclipse.jgit.internal.storage.dfs.InMemoryRepository;
@@ -109,7 +110,7 @@
     return res;
   }
 
-  private String buildJsonRaw(String path, String queryString) throws Exception {
+  private String buildJsonRaw(String path, @Nullable String queryString) throws Exception {
     String fmt = "format=JSON";
     queryString = Strings.isNullOrEmpty(queryString) ? fmt : fmt + "&" + queryString;
     FakeHttpServletResponse res = buildResponse(path, queryString, SC_OK);