Upgraded Gradle plugin

build.gradle.kts

@@ -21,7 +21,7 @@ buildscript {
     dependencies {
         classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:${com.unciv.build.BuildConfig.kotlinVersion}")
         classpath("de.richsource.gradle.plugins:gwt-gradle-plugin:0.6")
-        classpath("com.android.tools.build:gradle:3.6.3")
+        classpath("com.android.tools.build:gradle:4.0.0")
         classpath("com.mobidevelop.robovm:robovm-gradle-plugin:2.3.1")
 
         // This is for wrapping the .jar file into a standalone executable

core/src/com/unciv/ui/pickerscreens/TechPickerScreen.kt

@@ -154,6 +154,8 @@ class TechPickerScreen(internal val civInfo: CivilizationInfo, centerOnTech: Tec
         lines.clear()
 
         for (tech in civInfo.gameInfo.ruleSet.technologies.values) {
+            if(!techNameToButton.containsKey(tech.name))
+                throw Exception("tech ${tech.name} not found!")
             val techButton = techNameToButton[tech.name]!!
             for (prerequisite in tech.prerequisites) {
                 val prerequisiteButton = techNameToButton[prerequisite]!!

gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,6 @@
-#Sat Apr 25 23:34:18 IDT 2020
+#Mon Jun 01 02:27:12 IDT 2020
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-5.6.4-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.1.1-all.zip