treevalue graph cli cannot import the trees

[HansBug]

As the title said, it imports nothing and no error displayed. After setting PYTHONPATH=.${PYTHONPATH}, everything is okay. I seems to have something with hbutils library.

# test_main.py
from treevalue import TreeValue

t1 = TreeValue({
    'a': 2, 'b': 3,
    'x': {
        'c': 5, 'd': 7,
    }
})
t2 = TreeValue({
    't1': t1, 'a': 4, 'x': {'c': 5}
})
t2.x.d = t2

# command line
treevalue graph -t test_main.t1 -o test_graph.gv