no filter named tojson modify jinja2 / filters,py

filters.py

This is the error I got:

def join_path(self, template, parent):
\n in template()
\nTemplateAssertionError: no filter named 'tojson'\n

I tried different versions of jinja2, but the error remained. 

ref:
https://github.com/pallets/jinja/pull/456/commits/7b4393dc86f17d67e1711cd9aa02ff40366519b4


i was using pixiedust_node and it would not make a graph stating 'to_json' did not exist.
FYI - a window pops up and you must define the graph / plot parameters. It works fine 
on Ubuntu 16.04 python2.7 using jinja2 VERSION 2.8

in the file      ..../jinja2/filters.py
Create the def do_json(value): function and add iot right above the def do_round(value,  fuction


Example:

def do_json(value):
    """A filter that outputs Python objects as JSON"""
    import json
    return json.dumps(value)

-- this bottom function exists --- place do_json above it --
def do_round(value, precision=0, method='common'):
    """Round the number to a given precision. The first
    parameter specifies the precision (default is ``0``), 



Then add ( 'to_json':       do_json,  )  to the definitions on the bottom of the page:

Example:
      'wordcount':            do_wordcount,		     
      'wordcount':            do_wordcount,
      'wordwrap':             do_wordwrap,		     
      'wordwrap':             do_wordwrap,
      'xmlattr':              do_xmlattr,		      
      'xmlattr':              do_xmlattr,
      'to_json':              do_json,