Fixes.

Author: trivialfis

src/common/common.h

@@ -85,7 +85,7 @@ namespace xgboost::common {
 
   auto first = str.find_first_not_of(" \t\n\r");
   if (first == std::string_view::npos) {
-    return "";
+    return {};
   }
   return str.substr(first);
 }
@@ -96,7 +96,7 @@ namespace xgboost::common {
   }
   auto last = str.find_last_not_of(" \t\n\r");
   if (last == std::string_view::npos) {
-    return "";
+    return {};
   }
   return str.substr(0, last + 1);
 }

tests/cpp/common/test_common.cc

@@ -36,7 +36,7 @@ TEST(Common, Split) {
     std::string str{chars};
     auto res_str = Split(str, ',');
     std::string_view view{chars};
-    auto res_view = Split(str, ',');
+    auto res_view = Split(view, ',');
     ASSERT_EQ(res_view.size(), res_str.size());
     ASSERT_EQ(res_view.size(), n);
     for (std::size_t i = 0; i < res_str.size(); ++i) {