CJSON can not compare NULL

[petrkr]

Based on comment in source code https://github.com/nodemcu/nodemcu-firmware/blob/dev/app/modules/cjson.c
I trying compare NULL from JSON response, but I always getting "false" even using suggested compare with cjson.null one.

Expected behavior

return True

Actual behavior

returns false

Test code

json_null_test = cjson.decode('null')
print (json_null_test == cjson.null)
false

print (json_null_test)
userdata: 0x00000000

print (cjson.null)
nil

NodeMCU version

NodeMCU 1.5.4.1+petrkr build 20161101 powered by Lua 5.1.4 on SDK 1.5.4.1(39cb9a32) based on NodeMCU - branch dev commit f0780e3

Hardware

NodeMCU Devkit 1.0 with ESP-12

[petrkr]

Found workaround for this issue:

cjson_null = cjson.decode('null') -- Define NULL object for compare 
json_null_test = cjson.decode('null') -- Parse real JSON
print (json_null_test == cjson_null) -- Compare with local variable
true

so I can use aswell in more complex JSON's

cjson_null = cjson.decode('null')
json_null_test = cjson.decode('{ "var1": "Test var string1", "null_var": null }')
print (json_null_test.null_var == cjson_null)
true

[pjsg]

The new sjson module has an explicit sjson.NULL symbol which contains the null value in use.