Support empty input description

Author: arjunsuresh

automation/script/doc.py

@@ -141,6 +141,10 @@ def generate_docs(script_repo, metadata, script_path, generic_inputs):
     script_variations = metadata.get('variations', {})
     default_version = metadata.get('default_version')
 
+    for k in script_input_mapping:
+        if k not in script_input_description:
+            script_input_description[k] = ''
+
     r = get_run_readme(
         tags_string,
         script_input_mapping,