make warn return empty string

CHANGELOG.md

@@ -10,6 +10,7 @@
 - When a jinja value is undefined, give a helpful error instead of failing with cryptic "cannot pickle ParserMacroCapture" errors ([#2110](https://github.com/fishtown-analytics/dbt/issues/2110), [#2184](https://github.com/fishtown-analytics/dbt/pull/2184))
 - Added timeout to registry download call ([#2195](https://github.com/fishtown-analytics/dbt/issues/2195), [#2228](https://github.com/fishtown-analytics/dbt/pull/2228))
 - When a macro is called with invalid arguments, include the calling model in the output ([#2073](https://github.com/fishtown-analytics/dbt/issues/2073), [#2238](https://github.com/fishtown-analytics/dbt/pull/2238))
+- When a warn exception is not in a jinja do block, return an empty string instead of None ([#2222](https://github.com/fishtown-analytics/dbt/issues/2222))
 
 Contributors:
  - [@raalsky](https://github.com/Raalsky) ([#2224](https://github.com/fishtown-analytics/dbt/pull/2224), [#2228](https://github.com/fishtown-analytics/dbt/pull/2228))

core/dbt/exceptions.py

@@ -819,7 +819,8 @@ def warn_or_raise(exc, log_fmt=None):
 def warn(msg, node=None):
  # there's no reason to expose log_fmt to macros - it's only useful for
  # handling colors
- return warn_or_error(msg, node=node)
+ warn_or_error(msg, node=node)
+ return ""
 
 
 # Update this when a new function should be added to the