Minor gradle script changes

build.gradle

@@ -2,12 +2,6 @@ import java.nio.file.Paths
 
 // Top-level build file where you can add configuration options common to all sub-projects/modules.
 
-def props = new Properties()
-def configPath = project.hasProperty('configPath') ?
-        new File(project.configPath) : rootProject.file('config.prop')
-if (configPath.exists())
-    configPath.withInputStream { is -> props.load(is) }
-
 buildscript {
     ext.vKotlin = '1.3.72'
     ext.vNav = '2.3.0'
@@ -33,6 +27,13 @@ task clean(type: Delete) {
     delete rootProject.buildDir
 }
 
+String.metaClass.toFile = { new File(this) }
+def configFile = rootProject.findProperty('configPath')?.toFile() ?: rootProject.file('config.prop')
+if (!configFile.exists())
+    throw new GradleException("Please setup config.prop")
+
+def props = new Properties()
+configFile.withInputStream { is -> props.load(is) }
 ext.props = props
 
 subprojects {
@@ -98,17 +99,19 @@ subprojects {
             android {
                 signingConfigs {
                     config {
+                        if (props.containsKey('keyStore')) {
                             storeFile new File(props['keyStore'])
                             storePassword props['keyStorePass']
                             keyAlias props['keyAlias']
                             keyPassword props['keyPass']
                         }
                     }
+                }
 
                 buildTypes {
                     debug {
                         // If keystore exists, sign the APK with custom signature
-                        if (signingConfigs.config.storeFile.exists())
+                        if (signingConfigs.config.storeFile?.exists())
                             signingConfig signingConfigs.config
                     }
                     release {