PrereqScanner patch

diff --git a/lib/Perl/PrereqScanner.pm b/lib/Perl/PrereqScanner.pm
index 1c1a81e..55e2570 100644
--- a/lib/Perl/PrereqScanner.pm
+++ b/lib/Perl/PrereqScanner.pm
@@ -60,6 +60,7 @@ Version::Requirements object describing the modules it requires.
 sub scan_string {
   my ($self, $str) = @_;
   my $ppi = PPI::Document->new( \$str );
+  return Version::Requirements->new unless defined $ppi;
   return $self->scan_ppi_document( $ppi );
 }
 
@@ -76,6 +77,7 @@ Version::Requirements object describing the modules it requires.
 sub scan_file {
   my ($self, $path) = @_;
   my $ppi = PPI::Document->new( $path );
+  return Version::Requirements->new unless defined $ppi;
   return $self->scan_ppi_document( $ppi );
 }