Don't trim attribute values when field.max_length is None

Prevents 'TypeError: unorderable types: int() > NoneType()' in
_set_attribute when field.max_length = None

Some Django field classes do not set a max_length attribute, such as
IntegerField and PositiveIntegerField. The max_length attribute of these
classes is None (inherited from their parent class, Field).

Author: justinsg

djangosaml2/backends.py

@@ -272,7 +272,7 @@ def _set_attribute(self, obj, attr, value):
         Return True if the attribute was changed and False otherwise.
         """
         field = obj._meta.get_field(attr)
-        if len(value) > field.max_length:
+        if field.max_length is not None and len(value) > field.max_length:
             cleaned_value = value[:field.max_length]
             logger.warn('The attribute "%s" was trimmed from "%s" to "%s"',
                         attr, value, cleaned_value)