Restore NUL convention for helper name

src/constants.js

@@ -2,4 +2,6 @@ export const INLINE = {};
 export const RUNTIME = {};
 export const EXTERNAL = {};
 
-export const HELPERS = 'rollupPluginBabelHelpers';
+// NOTE: DO NOT REMOVE the null character `\0` as it may be used by other plugins
+// e.g. https://github.com/rollup/rollup-plugin-node-resolve/blob/313a3e32f432f9eb18cc4c231cc7aac6df317a51/src/index.js#L74
+export const HELPERS = '\0rollupPluginBabelHelpers';

test/test.js

@@ -5,7 +5,7 @@ var SourceMapConsumer = require( 'source-map' ).SourceMapConsumer;
 var babelPlugin = require( '..' );
 
 // from ./src/constants
-var HELPERS = 'rollupPluginBabelHelpers';
+var HELPERS = '\0rollupPluginBabelHelpers';
 
 require( 'source-map-support' ).install();