Fix missing context error

[ockham]

Fix #46, according to my comment:

I think it would make sense if "our" useContext was consistent with React's and -- in the absence of a Provider -- returned the default value used when creating the context:

const MyContext = React.createContext(defaultValue);
[...]
The defaultValue argument is only used when a component does not have a matching Provider above it in the tree. This default value can be helpful for testing components in isolation without wrapping them. Note: passing undefined as a Provider value does not cause consuming components to use defaultValue.

(source)

Testing instructions

• Verify that an Interactive Child block inside a Non-interactive Parent block works now:

• Verify that the Interactive Child block falls back to the default context passed when creating the context by applying the following patch:

diff --git a/src/context/counter.js b/src/context/counter.js
index 6061f47..0fa0325 100644
--- a/src/context/counter.js
+++ b/src/context/counter.js
@@ -1,7 +1,7 @@
 import { createContext } from '@wordpress/element';
 
 if (typeof window.reactContext === 'undefined') {
-       window.reactContext = createContext(null);
+       window.reactContext = createContext(0);
 }
 window.reactContext.displayName = 'CounterContext';
 export default window.reactContext;
diff --git a/src/context/theme.js b/src/context/theme.js
index 8aefc8e..d63cc62 100644
--- a/src/context/theme.js
+++ b/src/context/theme.js
@@ -1,7 +1,7 @@
 import { createContext } from '@wordpress/element';
 
 if (typeof window.themeReactContext === 'undefined') {
-       window.themeReactContext = createContext(null);
+       window.themeReactContext = createContext('twentytwentytwo');
 }
 window.themeReactContext.displayName = 'ThemeContext';
 export default window.themeReactContext;

Result:

• Verify that the if there is an intermediate layer with an Interactive Parent block, its context continues to be respected by the child block:

[ockham]

The problem was that event.detail.Provider is undefined if no Provider is... provided 🙃 , and that we're expecting a function that we later call.

If we only add Provider if it is a function, we fix the bug and get the desired behavior (falling back to the argument passed to createContext) for free 🎉

[cbravobernal]

LGTM!