use the suggested way of signing the apk

.gitignore

@@ -1,10 +1,11 @@
 *.iml
+*.aab
 .gradle
 /local.properties
+/gradle.properties
 /.idea/
 .DS_Store
 /build
 /captures
-release.keystore
+keystore.jks
-signing.properties
+keystore.properties
-/library/build

app/build.gradle

@@ -2,6 +2,10 @@ apply plugin: 'com.android.application'
 apply plugin: 'kotlin-android'
 apply plugin: 'kotlin-android-extensions'
 
+def keystorePropertiesFile = rootProject.file("keystore.properties")
+def keystoreProperties = new Properties()
+keystoreProperties.load(new FileInputStream(keystorePropertiesFile))
+
 android {
     compileSdkVersion 28
     buildToolsVersion "28.0.3"
@@ -17,7 +21,12 @@ android {
     }
 
     signingConfigs {
-        release
+        release {
+            keyAlias keystoreProperties['keyAlias']
+            keyPassword keystoreProperties['keyPassword']
+            storeFile file(keystoreProperties['storeFile'])
+            storePassword keystoreProperties['storePassword']
+        }
     }
 
     buildTypes {
@@ -46,22 +55,3 @@ dependencies {
 
     implementation files('../libs/RootTools.jar')
 }
-
-Properties props = new Properties()
-def propFile = new File('signing.properties')
-if (propFile.canRead()) {
-    props.load(new FileInputStream(propFile))
-
-    if (props != null && props.containsKey('STORE_FILE') && props.containsKey('KEY_ALIAS') && props.containsKey('PASSWORD')) {
-        android.signingConfigs.release.storeFile = file(props['STORE_FILE'])
-        android.signingConfigs.release.storePassword = props['PASSWORD']
-        android.signingConfigs.release.keyAlias = props['KEY_ALIAS']
-        android.signingConfigs.release.keyPassword = props['PASSWORD']
-    } else {
-        println 'signing.properties found but some entries are missing'
-        android.buildTypes.release.signingConfig = null
-    }
-} else {
-    println 'signing.properties not found'
-    android.buildTypes.release.signingConfig = null
-}

keystore.properties_sample

@@ -0,0 +1,4 @@
+storePassword=123456
+keyPassword=abcdef
+keyAlias=myAlias
+storeFile=../keystore.jks

signing.properties_sample

@@ -1,3 +0,0 @@
-STORE_FILE=/path/to/your.keystore
-KEY_ALIAS=projectkeyalias
-PASSWORD=yourkeypass