fix: Allow falsely children in route config (#357)

src/makeRouteConfig.js

@@ -3,6 +3,12 @@ import React from 'react';
 
 function buildRouteConfig(node, routeConfig) {
   React.Children.forEach(node, child => {
+    // Falsy children get coerced to null. We check for this instead of
+    // implicit falsiness because we don't want to allow empty strings or 0.
+    if (child === null) {
+      return;
+    }
+
     invariant(
       React.isValidElement(child),
       '`%s` is not a valid React element',

test/__snapshots__/makeRouteConfig.test.js.snap

@@ -1,3 +1,5 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
 exports[`makeRouteConfig should error on non-element children 1`] = `"\`,\` is not a valid React element"`;
+
+exports[`makeRouteConfig should error on other falsy children 1`] = `"\`0\` is not a valid React element"`;

test/makeRouteConfig.test.js

@@ -202,6 +202,28 @@ describe('makeRouteConfig', () => {
     }).toThrowErrorMatchingSnapshot();
   });
 
+  it('should allow empty children', () => {
+    expect(() => {
+      makeRouteConfig(
+        <Route path="/" Component={AppPage}>
+          {false}
+          <Route path="foo" Component={FooPage} />
+        </Route>,
+      );
+    }).not.toThrow();
+  });
+
+  it('should error on other falsy children', () => {
+    expect(() => {
+      makeRouteConfig(
+        <Route path="/" Component={AppPage}>
+          {0}
+          <Route path="foo" Component={FooPage} />
+        </Route>,
+      );
+    }).toThrowErrorMatchingSnapshot();
+  });
+
   ['react-proxy', 'react-stand-in'].forEach(packageName => {
     it(`should work with proxies from ${packageName}`, () => {
       // eslint-disable-next-line global-require, import/no-dynamic-require