Replace NULL and Nullptr_t with nullptr and nullptr_t

[afabri]

Summary of Changes

Replace NULL and Nullptr_t with nullptr and nullptr_t

Release Management

• Affected package(s): all
• Issue(s) solved (if any): fix #0000

[lrineau]

Please try to compile the packages you modify, before pushing.

[afabri]

@maxGimeno ready for testing

[maxGimeno]

warnings

[maxGimeno]

/usr/local/include/CGAL/marching_tetrahedra_3.h:56:57: error: redefinition of
'T_Vertex'
typedef typename T_Vertex_iterator::value_type T_Vertex;
^
/usr/local/include/CGAL/marching_tetrahedra_3.h:52:57: note: previous definition
is here
typedef typename T_Vertex_iterator::value_type T_Vertex;

[lrineau]

The header file Skin_surface_3/include/CGAL/marching_tetrahedra_3.h still does not compile:

In file included from /home/travis/build/CGAL/cgal/Skin_surface_3/include/CGAL/mesh_skin_surface_3.h:28:
/home/travis/build/CGAL/cgal/Skin_surface_3/include/CGAL/marching_tetrahedra_3.h:144:26: error: use of undeclared identifier 'Cell_handle'
    CGAL_assertion(ch != Cell_handle());
                         ^
/home/travis/build/CGAL/cgal/Skin_surface_3/include/CGAL/marching_tetrahedra_3.h:152:28: error: use of undeclared identifier 'Cell_handle'
      CGAL_assertion(ch != Cell_handle());
                           ^
2 errors generated.

https://travis-ci.org/CGAL/cgal/jobs/544716145#L6488

[lrineau]

I have fixed the compilation issues in 67e73c2.

[maxGimeno]

Seems all good in https://cgal.geometryfactory.com/CGAL/testsuite/results-5.0-Ic-59.shtml