Firestore: Validate that at least one argument is provided for Cursor

google-cloud-clients/google-cloud-firestore/src/main/java/com/google/cloud/firestore/Query.java

@@ -336,6 +336,9 @@ private Cursor createCursor(
   private Cursor createCursor(List<FieldOrder> order, Object[] fieldValues, boolean before) {
     Cursor.Builder result = Cursor.newBuilder();
 
+    Preconditions.checkState(
+        fieldValues.length != 0, "At least one cursor value must be specified.");
+
     Preconditions.checkState(
         fieldValues.length <= order.size(),
         "Too many cursor values specified. The specified values must match the "

google-cloud-clients/google-cloud-firestore/src/test/java/com/google/cloud/firestore/ConformanceTest.java

@@ -106,6 +106,9 @@ private interface ConformanceTestCase extends Test, Describable {}
   /** If non-empty, only runs tests included in this set. */
   private final Set<String> includedTests = Collections.emptySet();
 
+  /** If true, prints debug information to System.out. */
+  private final boolean DEBUG_MODE = !includedTests.isEmpty();
+
   @Captor private ArgumentCaptor<CommitRequest> commitCapture;
 
   @Captor private ArgumentCaptor<BatchGetDocumentsRequest> getAllCapture;
@@ -386,8 +389,9 @@ public void run(TestResult testResult) {
             new Protectable() {
               @Override
               public void protect() throws Throwable {
-                // Uncomment to print the test protobuf:
-                // System.out.println(testDefinition);
+                if (DEBUG_MODE) {
+                  System.out.println(testDefinition);
+                }
 
                 switch (testDefinition.getTestCase()) {
                   case GET: