Improve castError handling of non strings (#13315)

This pull removes castError from reduxRoutine and just passes along the value thrown instead of potentially coercing to an error.  

- Exposes values to consuming code.
- Less opinionated about what happens with the error.

packages/redux-routine/CHANGELOG.md

@@ -2,7 +2,9 @@
 
 ### Bug Fixes
 
-- Fix unhandled promise rejection error caused by returning null from registered generator ([#13314](https://github.com/WordPress/gutenberg/pull/13314)
+- Fix unhandled promise rejection error caused by returning null from registered generator ([#13314](https://github.com/WordPress/gutenberg/pull/13314))
+- The middleware will no longer attempt to coerce an error to an instance of `Error`, and instead passes through the thrown value directly. This resolves issues where an `Error` would be thrown when the underlying values were not of type `Error` or `string` (e.g. a thrown object) and the message would end up not being useful (e.g. `[Object object]`).
+([#13315](https://github.com/WordPress/gutenberg/pull/13315)) 
 
 ## 3.0.3 (2018-10-19)
 

packages/redux-routine/src/runtime.js

@@ -8,7 +8,6 @@ import isPromise from 'is-promise';
 /**
  * Internal dependencies
  */
-import castError from './cast-error';
 import { isActionOfType, isAction } from './is-action';
 
 /**
@@ -27,10 +26,7 @@ export default function createRuntime( controls = {}, dispatch ) {
 		const routine = control( value );
 		if ( isPromise( routine ) ) {
 			// Async control routine awaits resolution.
-			routine.then(
-				yieldNext,
-				( error ) => yieldError( castError( error ) ),
-			);
+			routine.then( yieldNext, yieldError );
 		} else {
 			next( routine );
 		}

packages/redux-routine/src/test/index.js

@@ -61,7 +61,7 @@ describe( 'createMiddleware', () => {
 			try {
 				yield { type: 'WAIT_FAIL' };
 			} catch ( error ) {
-				expect( error.message ).toBe( 'Message' );
+				expect( error ).toBe( 'Message' );
 			}
 		}