Type error when building for macOS

[fred-corp]

When using the build script for macOS, there is a type error :

 16:33:16[CEST] ~/Downloads/sigrok-util/cross-compile/macosx
$ ./sigrok-native-macosx

Cloning into 'libserialport'...
remote: Enumerating objects: 57, done.
remote: Counting objects: 100% (57/57), done.
remote: Compressing objects: 100% (43/43), done.
remote: Total 57 (delta 15), reused 40 (delta 14), pack-reused 0
Receiving objects: 100% (57/57), 105.96 KiB | 4.82 MiB/s, done.
Resolving deltas: 100% (15/15), done.
autoreconf: export WARNINGS=

[...]

sigrok/core/classes_wrap.cpp:8171:19: warning: result of comparison against a string literal is
      unspecified (use an explicit string comparison function instead) [-Wstring-compare]
 8171 |     else if (type == G_VARIANT_TYPE_INT32 && PyInt_Check(input))
      |                   ^  ~~~~~~~~~~~~~~~~~~~~
sigrok/core/classes_wrap.cpp:8173:19: warning: result of comparison against a string literal is
      unspecified (use an explicit string comparison function instead) [-Wstring-compare]
 8173 |     else if (type == G_VARIANT_TYPE_UINT32 && PyInt_Check(input))
      |                   ^  ~~~~~~~~~~~~~~~~~~~~~
sigrok/core/classes_wrap.cpp:62618:12: error: cannot initialize return object of type 'int' with an
      rvalue of type 'std::nullptr_t'
 62618 |     return nullptr;
       |            ^~~~~~~
7 warnings and 1 error generated.
error: command '/usr/bin/g++' failed with exit code 1
make[1]: *** [bindings/python/timestamp] Error 1
make: *** [all] Error 2

 16:34:50[CEST] ~/Downloads/sigrok-util/cross-compile/macosx
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