updated message and pass undefined

Author: Shailendra Gupta

packages/react-reconciler/src/ReactFiberBeginWork.new.js

@@ -2815,7 +2815,7 @@ function updateContextProvider(
       if (!hasWarnedAboutUsingNoValuePropOnContextProvider) {
         hasWarnedAboutUsingNoValuePropOnContextProvider = true;
         console.error(
-          'The prop `value` is required in `Context.Provider`, have you misspelled it',
+          'The `value` prop is required for the `<Context.Provider>`. Did you misspell it or forget to pass it?',
         );
       }
     }

packages/react-reconciler/src/ReactFiberBeginWork.old.js

@@ -2812,7 +2812,7 @@ function updateContextProvider(
       if (!hasWarnedAboutUsingNoValuePropOnContextProvider) {
         hasWarnedAboutUsingNoValuePropOnContextProvider = true;
         console.error(
-          'The prop `value` is required in `Context.Provider`, have you misspelled it',
+          'The `value` prop is required for the `<Context.Provider>`. Did you misspell it or forget to pass it?',
         );
       }
     }

packages/react-reconciler/src/__tests__/ReactNewContext-test.js

@@ -1097,7 +1097,7 @@ describe('ReactNewContext', () => {
       );
 
       expect(() => expect(Scheduler).toFlushWithoutYielding()).toErrorDev(
-        'The prop `value` is required in `Context.Provider`, have you misspelled it',
+        'The `value` prop is required for the `<Context.Provider>`. Did you misspell it or forget to pass it?',
         {
           withoutStack: true,
         },

packages/react/src/__tests__/ReactContextValidator-test.js

@@ -263,13 +263,13 @@ describe('ReactContextValidator', () => {
 
     class Component extends React.Component {
       render() {
-        return <TestContext.Provider value={null} />;
+        return <TestContext.Provider value={undefined} />;
       }
     }
 
     expect(() => ReactTestUtils.renderIntoDocument(<Component />)).toErrorDev(
       'Warning: Failed prop type: The prop `value` is marked as required in ' +
-        '`Context.Provider`, but its value is `null`.\n' +
+        '`Context.Provider`, but its value is `undefined`.\n' +
         '    in Component (at **)',
     );
   });