Problem adding wrapper method to REST_StringHelper

I am trying to add a wrapper method StringToTimeStamp for REST_StringHelper::ToTime method. Just as follows:

time_t ToTime(string time);
/// A method to convert a date/time formatted string to a timestamp. See also REST_StringHelper::ToTime.
time_t StringToTimeStamp(string time) { return ToTime(time); }

However, I get the following compilation error saying there is multiple method definition. Any idea of the reason?

[  2%] Linking CXX shared library libRestTools.so
CMakeFiles/RestTools.dir/resttools/src/TRestReflector.cxx.o: In function `REST_StringHelper::StringToTimeStamp(std::__cxx11::basic
_string<char, std::char_traits<char>, std::allocator<char> >)':
TRestReflector.cxx:(.text+0x20): multiple definition of `REST_StringHelper::StringToTimeStamp(std::__cxx11::basic_string<char, std
::char_traits<char>, std::allocator<char> >)'
CMakeFiles/RestTools.dir/resttools/src/TRestDataBase.cxx.o:TRestDataBase.cxx:(.text+0x2ab0): first defined here
CMakeFiles/RestTools.dir/resttools/src/TRestStringHelper.cxx.o: In function `REST_StringHelper::StringToTimeStamp(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)':
TRestStringHelper.cxx:(.text+0x1b80): multiple definition of `REST_StringHelper::StringToTimeStamp(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)'
CMakeFiles/RestTools.dir/resttools/src/TRestDataBase.cxx.o:TRestDataBase.cxx:(.text+0x2ab0): first defined here
CMakeFiles/RestTools.dir/__/__/rootdict/CINT_TRestStringHelper.cxx.o: In function `REST_StringHelper::StringToTimeStamp(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)':
CINT_TRestStringHelper.cxx:(.text+0x0): multiple definition of `REST_StringHelper::StringToTimeStamp(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)'
CMakeFiles/RestTools.dir/resttools/src/TRestDataBase.cxx.o:TRestDataBase.cxx:(.text+0x2ab0): first defined here
CMakeFiles/RestTools.dir/resttools/src/TRestSystemOfUnits.cxx.o: In function `REST_StringHelper::StringToTimeStamp(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)':
TRestSystemOfUnits.cxx:(.text+0x0): multiple definition of `REST_StringHelper::StringToTimeStamp(std::__cxx11::basic_string<char,