QStringRef: fix trimmed() returning null strings on empty input

The QString API symmetry test strikes again, showing that this is
inconsistent with both QString and QByteArray, which both return empty
for empty inputs.

The fix actually makes the implementation simpler.

Extend the QStringRef test to cover null inputs, too. I can't merge
the trimmed() test in the API symmetry test until everything is
actually consistent.

[ChangeLog][QtCore][QStringRef] trimmed() now returns an empty
string-ref for an empty input. Before, it would return a null one.

Change-Id: I6b35c5f498053c4e15a4a9dd465bc696258e7393
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Anton Kudryavtsev <antkudr@mail.ru>

1 files changed, 3 insertions, 1 deletions

diff --git a/tests/auto/corelib/tools/qstringref/tst_qstringref.cpp b/tests/auto/corelib/tools/qstringref/tst_qstringref.cpp
index d2374fe0ae..473f563f9b 100644
--- a/tests/auto/corelib/tools/qstringref/tst_qstringref.cpp
+++ b/tests/auto/corelib/tools/qstringref/tst_qstringref.cpp
@@ -1862,7 +1862,9 @@ void tst_QStringRef::double_conversion()
 
 void tst_QStringRef::trimmed()
 {
-    QString a;
+    QVERIFY(QStringRef().trimmed().isNull());
+    QString a = "";
+    QVERIFY(!QStringRef(&a).trimmed().isNull());
     QStringRef b;
     a = "Text";
     b = a.leftRef(-1);