The following code:

#include <sstream>
int main() {
    std::stringstream sstr;
    sstr << "Hello, World!\n"
}

is marked as an error (full message is attached):

Semantic Issue
5:10: error: invalid operands to binary expression ('std::stringstream' (aka 'basic_stringstream<char>') and 'const char *')
...

However it compiles without any errors.