# Buggy code
def merge_domaindata(self, docnames, otherdata):
    # type: (List[unicode], Dict) -> None
    self.data["root_symbol"].merge_with(otherdata["root_symbol"], docnames, self.env)
    ourNames = self.data["names"]
    for name, docname in otherdata["names"].items():
        if docname in docnames:
            if name in ourNames:
                msg = __(
                    "Duplicate declaration, also defined in '%s'.\n"
                    "Name of declaration is '%s'."
                )
                msg = msg % (ourNames[name], name)
                logger.warning(msg, location=docname)
            else:
                ourNames[name] = docname


# Traceback (AttributeError)
# Sphinx version: 1.8.0b1
# Python version: 2.7.13 (CPython)
# Docutils version: 0.14
# Jinja2 version: 2.10
# Last messages:
#   writing output... [ 18%] api/classsimgrid_1_1s4u_1_1Actor
#   writing output... [ 27%] api/dir_include
#   writing output... [ 36%] api/file_include_the_code.hpp
#   writing output... [ 45%] api/file_view_hierarchy
#   writing output... [ 54%] api/library_root
#   writing output... [ 63%] api/namespace_simgrid
#   writing output... [ 72%] api/namespace_simgrid__s4u
#   writing output... [ 81%] api/program_listing_file_include_the_code.hpp
#   writing output... [ 90%] api/unabridged_api
#   writing output... [100%] index
# Loaded extensions:
#   sphinx.ext.mathjax (1.8.0b1) from /home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/sphinx/ext/mathjax.pyc
#   alabaster (0.7.11) from /home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/alabaster/__init__.pyc
#   breathe (4.10.0) from /home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/breathe/__init__.pyc
#   exhale (0.2.0) from /home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/exhale/__init__.pyc
Traceback (most recent call last):
File "/home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/sphinx/cmd/build.py", line 304, in build_main
app.build(args.force_all, filenames)
File "/home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/sphinx/application.py", line 341, in build
self.builder.build_update()
File "/home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/sphinx/builders/__init__.py", line 350, in build_update
len(to_build))
File "/home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/sphinx/builders/__init__.py", line 415, in build
self.write(docnames, list(updated_docnames), method)
File "/home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/sphinx/builders/__init__.py", line 596, in write
self._write_serial(sorted(docnames))
File "/home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/sphinx/builders/__init__.py", line 604, in _write_serial
doctree = self.env.get_and_resolve_doctree(docname, self)
File "/home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/sphinx/environment/__init__.py", line 623, in get_and_resolve_doctree
self.apply_post_transforms(doctree, docname)
File "/home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/sphinx/environment/__init__.py", line 670, in apply_post_transforms
transformer.apply_transforms()
File "/home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/sphinx/transforms/__init__.py", line 90, in apply_transforms
Transformer.apply_transforms(self)
File "/home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/docutils/transforms/__init__.py", line 171, in apply_transforms
transform.apply(**kwargs)
File "/home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/sphinx/transforms/post_transforms/__init__.py", line 90, in apply
typ, target, node, contnode)
File "/home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/sphinx/domains/cpp.py", line 6767, in resolve_xref
target, node, contnode)[0]
File "/home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/sphinx/domains/cpp.py", line 6683, in _resolve_xref_inner
matchSelf=True, recurseInAnon=True)
File "/home/sven/Desktop/sphinx-cpp-cross-ref-bug/docs_exhale/venv/lib/python2.7/site-packages/sphinx/domains/cpp.py", line 4170, in find_declaration
candId = symbol.declaration.get_newest_id()
AttributeError: 'NoneType' object has no attribute 'get_newest_id'

# Fixed code
def merge_domaindata(self, docnames, otherdata):
    # type: (List[unicode], Dict) -> None
    # print("merge_domaindata:")
    # print("self")
    # print(self.data['root_symbol'].dump(0))
    # print("other:")
    # print(otherdata['root_symbol'].dump(0))

    self.data["root_symbol"].merge_with(otherdata["root_symbol"], docnames, self.env)
    ourNames = self.data["names"]
    for name, docname in otherdata["names"].items():
        if docname in docnames:
            if name in ourNames:
                msg = __(
                    "Duplicate declaration, also defined in '%s'.\n"
                    "Name of declaration is '%s'."
                )
                msg = msg % (ourNames[name], name)
                logger.warning(msg, location=docname)
            else:
                ourNames[name] = docname