split-select: fix OSX build

Clang is a bit stricter about what template definition it chooses
for mixed types that are normally possible to cast between.
Operations like std::find(int iterator, int iterator, enum) will fail,
as Clang won't implicitly cast an enum to an int here.

Change-Id: Ib2276c382ebf2b877e1045d32b1a9d0a1fa4d4a4
diff --git a/tools/split-select/TestRules.cpp b/tools/split-select/TestRules.cpp
index f980dc4..86ccd6a 100644
--- a/tools/split-select/TestRules.cpp
+++ b/tools/split-select/TestRules.cpp
@@ -75,7 +75,7 @@
         const char*, const char*,
         const sp<Rule>& actual, const Rule& expected) {
     const String8 expectedStr(expected.toJson());
-    const String8 actualStr(actual != NULL ? actual->toJson() : "");
+    const String8 actualStr(actual != NULL ? actual->toJson() : String8());
 
     if (expectedStr != actualStr) {
         return ::testing::AssertionFailure()