Detect and abort on empty morphologies

If given an empty string to parse yamlparse.load() will return None,
but this breaks code further down that expects to be dealing with a
dict. Raise an exception to avoid crashing.

Also, avoid catching 'Exception' when we only want to catch JSON
parse errors.

2 files changed, 9 insertions, 0 deletions

diff --git a/morphlib/morph2.py b/morphlib/morph2.py
index 26813925..a32ecbb9 100644
--- a/morphlib/morph2.py
+++ b/morphlib/morph2.py
@@ -74,6 +74,10 @@ class Morphology(object):
         except ValueError as e:  # pragma: no cover
             self._dict = morphlib.yamlparse.load(text)
             self._dumper = morphlib.yamlparse.dump
+
+        if data is None:
+            raise morphlib.YAMLError("Morphology is empty")
+
         self._set_defaults()
         self._validate_children()
 
diff --git a/morphlib/morph2_tests.py b/morphlib/morph2_tests.py
index 7a819556..a2c44753 100644
--- a/morphlib/morph2_tests.py
+++ b/morphlib/morph2_tests.py
@@ -164,6 +164,11 @@ class MorphologyTests(unittest.TestCase):
 
     ## Validation tests
 
+    def test_morphology_must_not_be_empty(self):
+        # Causes crashes if not handled, because code expecting a dict gets
+        # None instead.
+        self.assertRaises(morphlib.YAMLError, Morphology, '')
+
     def test_makes_max_jobs_be_an_integer(self):
         m = Morphology('''
             {