is null empty string regression in mapnik 2.2-pre

2.1.1.txt

'' != null:  False
0 != null:  False
null != null:  False
----------
'' = null:  False
0 = null:  False
null = null:  False
----------
'' != '':  False
0 != '':  True
null != '':  True
----------
'' = '':  True
0 = '':  False
null = '':  False

test-null-equality.py

import mapnik

def make(val):
    context = mapnik.Context()
    f = mapnik.Feature(context,0)
    f["prop"] = val
    return f

as_string = {
 None:'null',
 '':'\'\'',
 0:'0'
}
def debug(expr,val):
    val_string = as_string[val]
    print "%s: " % (expr.replace('[prop]',val_string)), mapnik.Expression(expr).evaluate(make(val))

print
debug("[prop] != null",'')
debug("[prop] != null",0)
debug("[prop] != null",None)
print '-'*10
debug("[prop] = null",'')
debug("[prop] = null",0)
debug("[prop] = null",None)
print '-'*10
debug("[prop] != ''",'')
debug("[prop] != ''",0)
debug("[prop] != ''",None)
print '-'*10
debug("[prop] = ''",'')
debug("[prop] = ''",0)
debug("[prop] = ''",None)

v2.1.0-1066-g37b74f1.txt

'' != null:  True
0 != null:  True
null != null:  False
----------
'' = null:  False
0 = null:  False
null = null:  True
----------
'' != '':  False
0 != '':  True
null != '':  True
----------
'' = '':  True
0 = '':  False
null = '':  False