Merge pull request #450 from Iterable/evan/MOB-5316-fix-gradle-config-to-inherit-values-from-parent

[MOB-5316] adds safeExtGet method to build.gradle

Author: evangreer91

android/build.gradle

@@ -3,16 +3,20 @@ apply plugin: 'com.android.library'
 import groovy.json.JsonSlurper
 
 android {
-    compileSdkVersion 28
+    compileSdkVersion safeExtGet('compileSdkVersion', 28)
 
     defaultConfig {
-        minSdkVersion 16
-        targetSdkVersion 28
+        minSdkVersion safeExtGet('minSdkVersion', 16)
+        targetSdkVersion safeExtGet('compileSdkVersion', 28)
 
         buildConfigField("String", "MODULE_VERSION", "\"${getModuleVersion()}\"")
     }
 }
 
+def safeExtGet(prop, fallback) {
+    rootProject.ext.has(prop) ? rootProject.ext.get(prop) : fallback
+}
+
 def getModuleVersion() {
     def jsonFile = file('../package.json')
     def parsedJson = new JsonSlurper().parseText(jsonFile.text)