fix: default to the UI locale instead of jvm default locale

Author: elPeiretti

src/main/java/com/flowingcode/vaadin/addons/localecombobox/LocaleComboBox.java

@@ -27,6 +27,7 @@
 import com.vaadin.flow.data.renderer.LitRenderer;
 import java.util.Collection;
 import java.util.Locale;
+import java.util.Optional;
 
 /**
  * Vaadin ComboBox extension that allows to choose between multiple locales.
@@ -76,7 +77,7 @@ public enum DisplayMode {
   }
 
   private DisplayMode displayMode = DisplayMode.DEFAULT;
-  private Locale customDisplayLocale = Locale.getDefault();
+  private Locale customDisplayLocale;
 
   /**
    * Indicates whether the flags should be displayed alongside the locale names.
@@ -124,7 +125,7 @@ public void setDisplayMode(DisplayMode displayMode) {
    * @param displayLocale the {@code Locale} to use for formatting.
    */
   public void setDisplayLocale(Locale displayLocale) {
-    this.customDisplayLocale = displayLocale == null ? Locale.getDefault() : displayLocale;
+    this.customDisplayLocale = displayLocale;
   }
 
   /**
@@ -178,13 +179,13 @@ private Locale getLocaleForDisplay() {
     switch (displayMode) {
 
       case CUSTOM:
-        return customDisplayLocale;
+        return Optional.ofNullable(customDisplayLocale).orElseGet(this::getLocale);
 
       case SELECTED:
-        return this.getValue() == null ? Locale.getDefault() : this.getValue();
+        return Optional.ofNullable(this.getValue()).orElseGet(this::getLocale);
 
       default:
-        return Locale.getDefault();
+        return this.getLocale();
     }
   }