[C++] Compiler error with GLog and unity build enabled

In file included from src/arrow/CMakeFiles/arrow_objlib.dir/Unity/unity_8_cxx.cxx:7:
In file included from /home/antoine/arrow/dev/cpp/src/arrow/util/logging.cc:29:
glog_ep-prefix/src/glog_ep/include/glog/logging.h:640:9: error: use of overloaded operator '<<' is ambiguous (with operand types 'std::ostream' (aka 'basic_ostream<char>') and 'const nullptr_t')
  (*os) << v;
  ~~~~~ ^  ~
glog_ep-prefix/src/glog_ep/include/glog/logging.h:696:3: note: in instantiation of function template specialization 'google::MakeCheckOpValueString<nullptr_t>' requested here
  MakeCheckOpValueString(comb.ForVar2(), v2);
  ^
glog_ep-prefix/src/glog_ep/include/glog/logging.h:720:1: note: in instantiation of function template specialization 'google::MakeCheckOpString<std::unordered_map<std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>, std::hash<std::string>, std::equal_to<std::__cxx11::basic_string<char> >, std::allocator<std::pair<const std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char> > > > *, nullptr_t>' requested here
DEFINE_CHECK_OP_IMPL(Check_NE, !=)  // Use CHECK(x == NULL) instead.
^
glog_ep-prefix/src/glog_ep/include/glog/logging.h:709:17: note: expanded from macro 'DEFINE_CHECK_OP_IMPL'
    else return MakeCheckOpString(v1, v2, exprtext); \
                ^
/home/antoine/arrow/dev/cpp/src/arrow/util/key_value_metadata.cc:75:3: note: in instantiation of function template specialization 'google::Check_NEImpl<std::unordered_map<std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char>, std::hash<std::string>, std::equal_to<std::__cxx11::basic_string<char> >, std::allocator<std::pair<const std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char> > > > *, nullptr_t>' requested here
  DCHECK_NE(out, nullptr);
  ^
glog_ep-prefix/src/glog_ep/include/glog/logging.h:996:31: note: expanded from macro 'DCHECK_NE'
#define DCHECK_NE(val1, val2) CHECK_NE(val1, val2)
                              ^
glog_ep-prefix/src/glog_ep/include/glog/logging.h:791:30: note: expanded from macro 'CHECK_NE'
#define CHECK_NE(val1, val2) CHECK_OP(_NE, !=, val1, val2)
                             ^
glog_ep-prefix/src/glog_ep/include/glog/logging.h:766:3: note: expanded from macro 'CHECK_OP'
  CHECK_OP_LOG(name, op, val1, val2, google::LogMessageFatal)
  ^
glog_ep-prefix/src/glog_ep/include/glog/logging.h:746:18: note: expanded from macro 'CHECK_OP_LOG'
         google::Check##name##Impl(                      \
                 ^
<scratch space>:101:1: note: expanded from here
Check_NEImpl
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/ostream:108:7: note: candidate function
      operator<<(__ostream_type& (*__pf)(__ostream_type&))
      ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/ostream:117:7: note: candidate function
      operator<<(__ios_type& (*__pf)(__ios_type&))
      ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/ostream:127:7: note: candidate function
      operator<<(ios_base& (*__pf) (ios_base&))
      ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/ostream:245:7: note: candidate function
      operator<<(const void* __p)
      ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/ostream:276:7: note: candidate function
      operator<<(__streambuf_type* __sb);
      ^