docker_build: fix JSON rewriting when some fields are null

Image generated by docker build might put "null" as entry
value in the JSON metadata. Ignore those value when doing
the deep copy to avoid error on assigning to "NoneType".

--
MOS_MIGRATED_REVID=100145909

1 files changed, 9 insertions, 1 deletions

diff --git a/tools/build_defs/docker/rewrite_json.py b/tools/build_defs/docker/rewrite_json.py
index 846bf5ceaa..850e321f1f 100644
--- a/tools/build_defs/docker/rewrite_json.py
+++ b/tools/build_defs/docker/rewrite_json.py
@@ -91,6 +91,14 @@ def Resolve(value, environment):
     os.environ = outer_env
 
 
+def DeepCopySkipNull(data):
+  """Do a deep copy, skipping null entry."""
+  if type(data) == type(dict()):
+    return dict((DeepCopySkipNull(k), DeepCopySkipNull(v))
+                for k, v in data.iteritems() if v is not None)
+  return copy.deepcopy(data)
+
+
 def RewriteMetadata(data, options):
   """Rewrite and return a copy of the input data according to options.
 
@@ -106,7 +114,7 @@ def RewriteMetadata(data, options):
   Raises:
     Exception: a required option was missing.
   """
-  output = copy.deepcopy(data)
+  output = DeepCopySkipNull(data)
 
   if not options.name:
     raise Exception('Missing required option: name')