Jacek Caban (@jacek) commented about dlls/mshtml/htmlelem.c:
+ + hres = variant_to_nsstr(pvarNS, FALSE, &ns_str); + if(FAILED(hres)) + return hres; + + nsAString_InitDepend(&name_str, strAttributeName); + nsAString_InitDepend(&value_str, NULL); + nsres = nsIDOMElement_GetAttributeNS(This->dom_element, &ns_str, &name_str, &value_str); + nsAString_Finish(&ns_str); + nsAString_Finish(&name_str); + + hres = return_nsstr_variant(nsres, &value_str, 0, AttributeValue); + if(FAILED(hres) || V_VT(AttributeValue) != VT_NULL) + return hres; + V_VT(AttributeValue) = VT_BSTR; + V_BSTR(AttributeValue) = SysAllocString(L""); I think this should just use NULL as BSTR value.
-- https://gitlab.winehq.org/wine/wine/-/merge_requests/538#note_5124