Don’t add /Info key in trailer if info dict is empty

The /Info key is forbidden by some variants, such as PDF/A-4.

Author: liZe

pydyf/__init__.py

@@ -467,7 +467,6 @@ def __init__(self):
 
         #: PDF :class:`Dictionary` containing the PDF’s metadata.
         self.info = Dictionary({})
-        self.add_object(self.info)
 
         #: PDF :class:`Dictionary` containing references to the other objects.
         self.catalog = Dictionary({
@@ -630,7 +629,9 @@ def write(self, output, version=b'1.7', identifier=False, compress=False):
             self.write_line(b'<<', output)
             self.write_line(f'/Size {len(self.objects)}'.encode(), output)
             self.write_line(b'/Root ' + self.catalog.reference, output)
-            self.write_line(b'/Info ' + self.info.reference, output)
+            if self.info:
+                self.add_object(self.info)
+                self.write_line(b'/Info ' + self.info.reference, output)
             if identifier:
                 data = b''.join(
                     obj.data for obj in self.objects if obj.free != 'f')