IDL: make optional arguments (without default) explicit sometimes

Source/modules/indexeddb/IDBCursor.cpp

Index: Source/modules/indexeddb/IDBCursor.cpp
diff --git a/Source/modules/indexeddb/IDBCursor.cpp b/Source/modules/indexeddb/IDBCursor.cpp
index 63468995c9be8390b953b75a50245a0bebc88216..9aa47fdc9cbc07aa72d366b08a9cd56ce4f63b77 100644
--- a/Source/modules/indexeddb/IDBCursor.cpp
+++ b/Source/modules/indexeddb/IDBCursor.cpp
@@ -152,7 +152,7 @@ void IDBCursor::advance(unsigned long count, ExceptionState& exceptionState)
 void IDBCursor::continueFunction(ScriptState* scriptState, const ScriptValue& keyValue, ExceptionState& exceptionState)
 {
     IDB_TRACE("IDBCursor::continue");
-    IDBKey* key = keyValue.isUndefined() || keyValue.isNull() ? nullptr : scriptValueToIDBKey(scriptState->isolate(), keyValue);
+    IDBKey* key = keyValue.isEmpty() || keyValue.isUndefined() || keyValue.isNull() ? nullptr : scriptValueToIDBKey(scriptState->isolate(), keyValue);
     if (key && !key->isValid()) {
         exceptionState.throwDOMException(DataError, IDBDatabase::notValidKeyErrorMessage);
         return;