Minor improvements (#21)

* Mark nullable fields, rely on ext

* Add kotlin gradle plugin note.

Author: michalchudziak

android/build.gradle

@@ -10,14 +10,13 @@ repositories {
 }
 
 android {
-    compileSdkVersion 28
+    compileSdkVersion safeExtGet('compileSdkVersion', 28)
 
     defaultConfig {
-        minSdkVersion 21
-        targetSdkVersion 28
-        versionCode 1
-        versionName "1.0.0"
+        minSdkVersion safeExtGet('minSdkVersion', 21)
+        targetSdkVersion safeExtGet('targetSdkVersion', 28)
     }
+
     lintOptions {
         abortOnError false
     }

docs/JAVA.md

@@ -2,6 +2,23 @@
 
 React Native Brownfield provides first-class support for Java.
 
+### Kotlin setup
+
+Even though the library provides a first-class Java support, it's written in Kotlin. To compile the project with React Native Brownfield, we need to make sure that our project's `build.gradle` file contains the required Gradle plugin. 
+
+```java
+buildscript {
+    ext {
+        ...
+        kotlinVersion = '1.3.31'
+    }
+    dependencies {
+        ...
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion"
+    }
+}
+```
+
 ### Linking
 
 The library is meant to work with [auto linking](https://github.com/react-native-community/cli/blob/master/docs/autolinking.md). In case you can't use this feature, please check out the following options:

example/java/build.gradle

@@ -16,7 +16,6 @@ buildscript {
     dependencies {
         classpath 'com.android.tools.build:gradle:3.4.1'
         classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion"
-
     }
 }
 

ios/ReactNativeBrownfield.h

@@ -9,7 +9,7 @@ NS_ASSUME_NONNULL_BEGIN
 }
 
 @property (nonatomic, copy) NSString *entryFile;
-@property (nonatomic, copy) NSString *fallbackResource;
+@property (nonatomic, copy, nullable) NSString *fallbackResource;
 @property (nonatomic, copy) NSString *bundlePath;
 @property (nonatomic) RCTBridge *bridge;
 

ios/ReactNativeViewController.h

@@ -5,7 +5,7 @@ NS_ASSUME_NONNULL_BEGIN
 @interface ReactNativeViewController : UIViewController
 
 @property (nonatomic, copy) NSString *moduleName;
-@property (nonatomic, copy) NSDictionary *initialProperties;
+@property (nonatomic, copy, nullable) NSDictionary *initialProperties;
 
 -(instancetype)initWithModuleName:(NSString *)moduleName;
 -(instancetype)initWithModuleName:(NSString *)moduleName andInitialProperties:(NSDictionary*)initialProperties;