Throw error from non-OK answer for better error handling

jme3-templates/src/com/jme3/gde/templates/utils/mavensearch/MavenApiVersionChecker.java

@@ -120,7 +120,7 @@ public class MavenApiVersionChecker implements MavenVersionChecker {
         CompletableFuture<T> result = client.sendAsync(request, BodyHandlers.ofString())
                 .thenApply((t) -> {
                     if (t.statusCode() != 200) {
-                        return null;
+                        throw new MavenVersionCheckException("Calling " + encodedURL + " not OK. API response " + t.statusCode() + "!");
                     }
 
                     return gson.fromJson(t.body(), clazz);

jme3-templates/src/com/jme3/gde/templates/utils/mavensearch/MavenVersionCheckException.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2009-2023 jMonkeyEngine
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * * Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * * Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ *
+ * * Neither the name of 'jMonkeyEngine' nor the names of its contributors
+ *   may be used to endorse or promote products derived from this software
+ *   without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package com.jme3.gde.templates.utils.mavensearch;
+
+/**
+ * Exception with Maven version check
+ */
+public class MavenVersionCheckException extends RuntimeException {
+
+    public MavenVersionCheckException(String message) {
+        super(message);
+    }
+
+}