fix error where an intermediate None value was breaking jinja2 for git

conda_build/metadata.py

@@ -451,7 +451,9 @@ def version(self):
         return res
 
     def build_number(self):
-        return int(self.get_value('build/number', 0))
+        number = self.get_value('build/number', 0)
+        # build number can come back as None if no setting (or jinja intermediate)
+        return int(number) if number else 0
 
     def ms_depends(self, typ='run'):
         res = []

tests/test-recipes/metadata/_git_describe_number_branch/meta.yaml

@@ -0,0 +1,11 @@
+package:
+  name: git_describe_number_branch
+  version: {{ GIT_DESCRIBE_TAG }}
+
+source:
+  git_url: https://github.com/conda/conda_build_test_recipe
+  git_branch: 1.20.2+1
+
+build:
+  number: {{ GIT_DESCRIBE_NUMBER }}
+  string: {{ GIT_BUILD_STR }}

tests/test_build_recipes.py

@@ -377,3 +377,15 @@ def test_patch():
                 lines = modified.readlines()
                 assert lines[0] == '43770\n'
         os.chdir(basedir)
+
+
+def test_git_describe_info_on_branch():
+    cmd = 'conda build --output {}'.format(os.path.join(metadata_dir, "_git_describe_number_branch"))
+    process = subprocess.Popen(cmd.split(),
+                    stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+    output, error = process.communicate()
+    test_path = os.path.join(sys.prefix, "conda-bld", subdir,
+                        "git_describe_number_branch-1.20.2-1_g82c6ba6.tar.bz2")
+    output = output.decode('utf-8').rstrip()
+    error = error.decode('utf-8')
+    assert test_path == output, error