update the gradle version and the kotlin version

build.gradle

@@ -1,8 +1,5 @@
-group 'ninja.javafx'
-version '1.1-SNAPSHOT'
-
 buildscript {
-    ext.kotlin_version = '1.0.4'
+    ext.kotlin_version = '1.3.72'
 
     repositories {
         mavenCentral()
@@ -12,18 +9,27 @@ buildscript {
     }
 }
 
-apply plugin: 'kotlin'
-apply plugin: 'application'
-
-mainClassName = 'ninja.javafx.smartcsv.fx.converter.ConverterFX'
+plugins {
+    id "org.jetbrains.kotlin.jvm" version "$kotlin_version" 
+    id 'application'
+    id 'org.openjfx.javafxplugin' version '0.0.8'
+}
 
 repositories {
     mavenCentral()
     jcenter()
 }
 
+javafx {
+    modules = [ 'javafx.controls', 'javafx.fxml' ]
+}
+
 dependencies {
     compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
     compile 'com.beust:klaxon:0.24'
     compile 'no.tornado:tornadofx:1.5.6'
 }
+
+group 'ninja.javafx'
+version '1.1-SNAPSHOT'
+mainClassName = 'ninja.javafx.smartcsv.fx.converter.ConverterFX'

gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-2.13-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.4.1-all.zip

src/main/kotlin/ninja/javafx/smartcsv/fx/converter/Converter.kt

@@ -85,11 +85,9 @@ class Converter(val name: String) {
 
     }
 
-    @Suppress("UNCHECKED_CAST")
     fun constraint(column : JsonObject, key : String, value: Any?) {
         if (value == null) return
-        val constraints = column["constraints"] as JsonObject? ?: JsonObject(HashMap<String, Any>())
-        column["constraints"] = constraints
+        val constraints = column.getOrPut("constraints") { JsonObject(mutableMapOf()) } as JsonObject
         constraints[key] = value
     }