Throw error in development mode when title is not a string

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ## [Unreleased]
 - Throw error in development mode when header navigation option is set to a string - a common mistake that would otherwise result in a cryptic error message.
 - Update react-navigation-drawer to 0.4.3 to fix `initialRouteParams` option
+- Throw error in development mode when title is not a string.
 
 ## [2.5.4] - [2018-06-27](https://github.com/react-navigation/react-navigation/releases/tag/2.5.4)
 ### Fixed

src/views/Header/Header.js

@@ -55,6 +55,15 @@ class Header extends React.PureComponent {
     if (typeof options.headerTitle === 'string') {
       return options.headerTitle;
     }
+
+    if (options.title && typeof options.title !== 'string' && __DEV__) {
+      throw new Error(
+        `Invalid title for route "${
+          scene.route.routeName
+        }" - title must be string or null, instead it was of type ${typeof options.title}`
+      );
+    }
+
     return options.title;
   }