AttributeError: 'NoneType' object has no attribute 'append'

[stmtstk]

Hi, All,

When I tried to convert from a six 2.1 content with some external_reference properties, an AttributeError has occurred.

At a create_references function in convert_stix.py, this library tried to info_source.add_reference(rt).

In add_reference function, it tried to append an argument value into a self.references property, however self.references is None.

I will recommend to insert a None check in add_reference, if self.references is None then self.references = [] and append a value.

[stmtstk]

Sorry...

A self.references.append(value) is in python-stix library. I should publish this issue in python-stix.

[rpiazza]

Hi @stmtstk,

We are planning to release a new version of the slider soon. In it, there is much improved code for handling external references. However, I'd like to make sure that the error you are hitting is handled by the new code. Can you send me the example STIX 2.x content that caused the error?

The python-stix code should probably handle this too. I will look into that - you don't need to.

[stmtstk]

I used master version library (not version 2.0.0).

In convert_stix.py, if an object contains a "created_by_ref" property, convert_bundle function calls process_created_by_ref (line: 1382). process_created_by_ref calls create_information_source function (line: 1171) due to generating an InformationSource object. However, in create_information_source, there are no references argument.

    if used_before:
        return InformationSource(identity=Identity(idref=identity_obj.id_))
    else:
        identity2x_tuple[1] = True
        return InformationSource(identity=identity_obj)

If InformationSource is called without a references argument, this references variable is None.

if STIX 2.x object contains a "external_references" property, "create_references" is called (line: 1384). In "create_references", if an external_references property contains an url and an object_type is not Indicator, call add_references (line: 1137) and an AttributeError occurs (because references is None).

I recommend to modify to generate an InformationSource object below.

    if used_before:
        return InformationSource(identity=Identity(idref=identity_obj.id_), references=References())
    else:
        identity2x_tuple[1] = True
        return InformationSource(identity=identity_obj, references=References())

[rpiazza]

Thanks @stmtstk

This fix looks great. I will be testing it and assuming no other problems, it will be included in the next release.

[rpiazza]

@emmanvg,

Can you look into the python-stix aspect of this issue?

I tested the fix suggested by @stmtsk, but if there are no references then you get a

            <stixCommon:References/>

in the STIX 1.x content, which I would like to avoid. Perhaps fixing the python-stix code is what is really needed.

[rpiazza]

Closing this. It should be fixed in python-stix - see https://github.com/STIXProject/python-stix/issues/366