improve datanode conversion

Author: burdoto

src/main/java/org/comroid/api/data/seri/DataNode.java

@@ -140,8 +140,8 @@ else if (this instanceof Object)
             return properties().collect(JSON.Object::new, (n, e) -> n.put(e.key, e.getValue().json()), Map::putAll);
         else if (this instanceof Array)
             return properties().collect(JSON.Array::new, (n, e) -> n.add(e.getValue().json()), List::addAll);
-        else if (this instanceof Value)
-            return Convertible.convert(this, JSON.Value.class);
+        else if (this instanceof Value<?> value)
+            return JSON.Value.convert(value);
         else return of(this).json();
     }
 

src/main/java/org/comroid/api/data/seri/adp/JSON.java

@@ -19,7 +19,6 @@
 import java.io.StringReader;
 import java.util.List;
 import java.util.Map;
-import java.util.Objects;
 import java.util.stream.Collectors;
 
 public enum JSON implements Serializer<JSON.Node> {
@@ -193,9 +192,9 @@ public static JSON.Object of(Map<String, java.lang.Object> map) {
         }
 
         @Override
-        public String toString() {
+        public String toSerializedString() {
             return map.entrySet().stream()
-                    .map(e -> "\"%s\": %s".formatted(e.getKey(), e.getValue().toString()))
+                    .map(e -> "\"%s\": %s".formatted(e.getKey(), e.getValue().toSerializedString()))
                     .collect(Collectors.joining(", ", "{", "}"));
         }
     }
@@ -210,9 +209,9 @@ public static JSON.Array of(List<java.lang.Object> list) {
         }
 
         @Override
-        public String toString() {
+        public String toSerializedString() {
             return list.stream()
-                    .map(Objects::toString)
+                    .map(DataNode::toSerializedString)
                     .collect(Collectors.joining(", ", "[", "]"));
         }
     }
@@ -231,9 +230,9 @@ public Value(@Nullable T value) {
         }
 
         @Override
-        public String toString() {
+        public @NotNull String toSerializedString() {
             // this method is a super-stub because it depends on the functionality of the underlying method
-            return super.toString();
+            return super.toSerializedString();
         }
     }
 }

src/main/java/org/comroid/api/func/ext/Convertible.java

@@ -3,8 +3,8 @@
 import org.comroid.annotations.Convert;
 import org.comroid.annotations.internal.Annotations;
 import org.comroid.api.func.util.Invocable;
-import org.comroid.api.info.Constraint;
 import org.jetbrains.annotations.ApiStatus.Experimental;
+import org.jetbrains.annotations.Contract;
 import org.jetbrains.annotations.NotNull;
 
 import java.lang.reflect.Modifier;
@@ -16,12 +16,12 @@
 public interface Convertible {
     @Experimental
     @SuppressWarnings("unchecked")
-    static <R> @NotNull R convert(Object it_, Class<? super R> target) {
+    @Contract("null, !null -> null; !null, !null -> _; !null, null -> fail")
+    static <R> R convert(Object it_, Class<? super R> target) {
         var it = it_ instanceof Supplier && Annotations.ignore(it_.getClass(), Convertible.class).isEmpty()
                  ? ((Supplier<?>) it_).get() : it_;
-        Constraint.notNull(it, "source object")
-                .setHint("check implementation")
-                .run();
+        if (it == null)
+            return null;
         if (target.isInstance(it))
             return (R) target.cast(it);
         return Stream.concat(Stream.of(target.getConstructors()),