Don't pass 'undefined' for missing optional parameters (#4064)

* Don't try do decode `undefined`
decodeURIComponent(undefined) is "undefined"

* add a test

* do not pass missing optional parameters at all

Author: jochenberger

modules/__tests__/Match-test.js

@@ -71,6 +71,24 @@ describe('Match', () => {
             })
           })
         })
+        it('does not pass optinal parameters if they do not occur in the URL', () => {
+          renderToString(
+            <Match
+              pattern="/:foo/:bar?"
+              location={{ pathname: '/foo' }}
+              component={(props) => {
+                expect(props).toEqual({
+                  params: { foo: 'foo' },
+                  isExact: true,
+                  pathname: '/foo',
+                  location: { pathname: '/foo' },
+                  pattern: '/:foo/:bar?'
+                })
+                return <div />
+              }}
+            />
+          )
+        })
       })
 
       describe('when matched partially', () => {

modules/matchPattern.js

@@ -22,7 +22,7 @@ const getMatcher = (pattern, exactly) => {
 }
 
 const parseParams = (pattern, match, keys) =>
-  match.slice(1).reduce((params, value, index) => {
+  match.slice(1).filter(value => value !== undefined).reduce((params, value, index) => {
     params[keys[index].name] = decodeURIComponent(value)
     return params
   }, {})