Use string.empty() instead of == ""

Author: Owen Jones

src/pointer-analysis/local_value_set.cpp

@@ -463,9 +463,7 @@ void local_value_sett::assign_rec(
       declared_on_type,
       suffix_without_subtype);
     std::string access_path_suffix=
-      suffix_without_subtype == "" ?
-      "[]" :
-      suffix_without_subtype;
+      suffix_without_subtype.empty() ? "[]" : suffix_without_subtype;
     access_path_entry_exprt newentry(
       access_path_suffix,
       function,