I have some XS to interface with a C API where one of the arguments is a pointer which may be null. However, calling it this way causes it to spit out the warning "Use of uninitialized value in subroutine entry". Example usage (names changes to protect the innocent): 
my $foo = undef;
my $bar = Foo::create_bar (\$foo);

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The XS is: 
struct bar*
create_bar(foo)
  struct type_foo* foo
  CODE:
    RETVAL = my_c_create_bar(foo);
  OUTPUT:
    RETVAL

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And, there's a type map: 
TYPEMAP
struct bar* T_OBJECT
struct type_foo* T_OBJECT

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I read Source of warning message: "Use of uninitialized value in subroutine entry" and that suggested that this warning could be encountered passing NULL to functions in the perl API, but in this case it's an external C library where, as I said, NULL is a perfectly valid value. Is there something I should be doing to communicate that NULL is okay?

In reply to Passing NULL pointer through XS without "Use of uninitialized value in subroutine entry" by kscaldef

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