#handle zero-length lists and tuples in convert_dtype (#57)

* #56 handle zero-length lists and tuples in convert_dtype

* #56 empty value test

* #56 fix return type when zero-length list passed to ObjectMapper.convert_dtype

src/hdmf/build/map.py

@@ -431,6 +431,8 @@ def convert_dtype(cls, spec, value):
                 ret = np.asarray(value).astype(dtype_func)
                 ret_dtype = ret.dtype.type
         elif isinstance(value, (tuple, list)):
+            if len(value) == 0:
+                return value, spec_dtype
             ret = list()
             for elem in value:
                 tmp, tmp_dtype = cls.convert_dtype(spec, elem)

tests/unit/build_tests/test_io_map.py

@@ -343,6 +343,14 @@ def test_build(self):
                                 attributes={'attr1': 'value1', 'attr2': 10})
         self.assertDictEqual(builder, expected)
 
+    def test_build_empty(self):
+        ''' Test default mapping functionality when no attributes are nested '''
+        container = Bar('my_bar', [], 'value1', 10)
+        builder = self.mapper.build(container, self.manager)
+        expected = GroupBuilder('my_bar', datasets={'data': DatasetBuilder('data', [])},
+                                attributes={'attr1': 'value1', 'attr2': 10})
+        self.assertDictEqual(builder, expected)
+
     def test_construct(self):
         builder = GroupBuilder('my_bar', datasets={'data': DatasetBuilder('data', list(range(10)))},
                                attributes={'attr1': 'value1', 'attr2': 10, 'data_type': 'Bar',