loader_tags_fragment.py

class IncludeNode(Node):
    context_key = '__include_context'

    # ... constructor etc.  ...

    def render(self, context):
        try:
            # ... template gets rendered here ...
        except Exception as e:
            if context.template.engine.debug:
                raise
            template_name = getattr(context, 'template_name', None) or 'unknown'
            warnings.warn(
                "Rendering {%% include '%s' %%} raised %s. In Django 2.1, "
                "this exception will be raised rather than silenced and "
                "rendered as an empty string." %
                (template_name, e.__class__.__name__),
                RemovedInDjango21Warning,
            )
            logger.warning(
                "Exception raised while rendering {%% include %%} for "
                "template '%s'. Empty string rendered instead.",
                template_name,
                exc_info=True,
            )
        return ''