chore: Solve Gradle 9 incompatibility issues (#2692)

backend/app/build.gradle

@@ -140,7 +140,7 @@ dependencies {
     /**
      * Conditional billing module
      */
-    if (rootProject.project(":billing-app").projectDir.exists()) {
+    if (gradle.ext.billingAppDirectory.exists()) {
         implementation(project(':billing-app'))
     }
 

backend/data/build.gradle

@@ -52,7 +52,6 @@ apply plugin: 'org.hibernate.orm'
 
 repositories {
     mavenCentral()
-    jcenter()
 }
 
 idea {

backend/testing/build.gradle

@@ -43,7 +43,6 @@ apply plugin: "kotlin-kapt"
 
 repositories {
     mavenCentral()
-    jcenter()
 }
 
 kotlin {

build.gradle

@@ -117,9 +117,8 @@ project(':server-app').afterEvaluate {
                 project(':ee-app').tasks.findByName("diffChangelog"),
         ]
 
-        def billingDiffChangelog = project(':billing-app').tasks.findByName("diffChangelog")
-
-        if (billingDiffChangelog != null) {
+        if (gradle.ext.billingAppDirectory.exists()) {
+            def billingDiffChangelog = project(':billing-app').tasks.findByName("diffChangelog")
             finalizedBy.add(billingDiffChangelog)
         }
 

settings.gradle

@@ -83,11 +83,18 @@ project(':server-app').projectDir = new File('backend/app')
 include ':data'
 project(':data').projectDir = new File('backend/data')
 
-include ':billing-app'
-project(':billing-app').projectDir = new File('../billing/app')
+gradle.ext.billingAppDirectory = new File('../billing/app')
+gradle.ext.billingTestDirectory = new File('../billing/tests')
 
-include ':billing-test'
-project(':billing-test').projectDir = new File('../billing/tests')
+if (gradle.ext.billingAppDirectory.exists()) {
+    include ':billing-app'
+    project(':billing-app').projectDir = gradle.ext.billingAppDirectory
+}
+
+if (gradle.ext.billingTestDirectory.exists()) {
+    include ':billing-test'
+    project(':billing-test').projectDir = gradle.ext.billingTestDirectory
+}
 
 include ':testing'
 project(':testing').projectDir = new File('backend/testing')