Refactor calls to UIManagerHelper.getUIManager

Summary:
This diff refactors the usages of UIManagerHelper.getUIManager() to make sure we always consider null objects.
Some of the callsites were throwing a NullPointerExcetpion, now they throw a more explicit exception.

changelog: [internal]

Reviewed By: makovkastar

Differential Revision: D19383064

fbshipit-source-id: 1806a37528e80cab1c8fdff5eb631aaf47bde819

ReactAndroid/src/main/java/com/facebook/react/uimanager/UIManagerModule.java

@@ -680,22 +680,18 @@ public class UIManagerModule extends ReactContextBaseJavaModule
       int reactTag, Dynamic commandId, @Nullable ReadableArray commandArgs) {
     // TODO: this is a temporary approach to support ViewManagerCommands in Fabric until
     // the dispatchViewManagerCommand() method is supported by Fabric JS API.
+    @Nullable
+    UIManager uiManager =
+        UIManagerHelper.getUIManager(
+            getReactApplicationContext(), ViewUtil.getUIManagerType(reactTag));
+    if (uiManager == null) {
+      return;
+    }
+
     if (commandId.getType() == ReadableType.Number) {
-      final int commandIdNum = commandId.asInt();
-      UIManager uiManager =
-          UIManagerHelper.getUIManager(
-              getReactApplicationContext(), ViewUtil.getUIManagerType(reactTag));
-      if (uiManager != null) {
-        uiManager.dispatchCommand(reactTag, commandIdNum, commandArgs);
-      }
+      uiManager.dispatchCommand(reactTag, commandId.asInt(), commandArgs);
     } else if (commandId.getType() == ReadableType.String) {
-      final String commandIdStr = commandId.asString();
-      UIManager uiManager =
-          UIManagerHelper.getUIManager(
-              getReactApplicationContext(), ViewUtil.getUIManagerType(reactTag));
-      if (uiManager != null) {
-        uiManager.dispatchCommand(reactTag, commandIdStr, commandArgs);
-      }
+      uiManager.dispatchCommand(reactTag, commandId.asString(), commandArgs);
     }
   }