Avoid returning null for CoreRunner steps

Author: shs96c

java/server/src/org/openqa/selenium/server/htmlrunner/NonReflectiveSteps.java

@@ -115,7 +115,7 @@ public NextStepDecorator execute(Selenium selenium, TestState state) {
 
     steps.put("store", (((locator, value) -> ((selenium, state) -> {
       state.store(state.expand(locator), state.expand(value));
-      return null;
+      return NextStepDecorator.IDENTITY;
     }))));
 
     return steps.build();

java/server/src/org/openqa/selenium/server/htmlrunner/ReflectivelyDiscoveredSteps.java

@@ -156,7 +156,7 @@ private static ImmutableMap<String, CoreStepFactory> discover() {
             String value = state.expand(val);
             Object toStore = invokeMethod(method, selenium, buildArgs(method, locator, value));
             state.store(locator, toStore);
-            return null;
+            return NextStepDecorator.IDENTITY;
           }));
       }