json: Improve error handling and adding ability to limit log output.

recipe_modules/json/example.py

Index: recipe_modules/json/example.py
diff --git a/recipe_modules/json/example.py b/recipe_modules/json/example.py
index 5ecc78d6d7aad543025828794f2990d86d2eb689..99aadb86fe809d1c37e3c15bcbd0128648057ad7 100644
--- a/recipe_modules/json/example.py
+++ b/recipe_modules/json/example.py
@@ -78,6 +78,21 @@ def RunSteps(api):
   ])
   assert step_result.json.output is None
 
+  # empty json data is explicit
+  step_result = api.step('empty json', [
+    'python', api.resource('cool_script.py'),
+    '',
+    api.json.output(),
+  ])
+  assert step_result.json.output is None
+
+  # empty json data is explicit
+  step_result = api.step('None json', [
+    'python', api.resource('cool_script.py'),
+    api.json.output(),
+  ])
+  assert step_result.json.output is None
+
 
 def GenTests(api):
   yield (
@@ -96,4 +111,8 @@ def GenTests(api):
       'invalid json',
       api.json.invalid('{"here is some total\ngarbage'),
     )
+    + api.step_data(
+      'empty json',
+      api.json.invalid(''),
+    )
   )