fix(core): MapNode#getString should check if the node is StringRepresentable

Author: Siroshun09

core/src/main/java/com/github/siroshun09/configapi/core/node/MapNode.java

@@ -294,7 +294,7 @@ public sealed interface MapNode extends CommentableNode<Map<Object, Node<?>>> pe
      * @return the {@link String} to which the specified key is mapped, or the specified value if the key is not mapped to {@link StringValue}
      */
     default @NotNull String getString(@NotNull Object key, @NotNull String def) {
-        return this.raw(key) instanceof StringValue value ? value.asString() : def;
+        return this.raw(key) instanceof StringRepresentable value ? value.asString() : def;
     }
 
     /**
@@ -304,7 +304,7 @@ public sealed interface MapNode extends CommentableNode<Map<Object, Node<?>>> pe
      * @return the {@link String} to which the specified key is mapped, or {@code null} if the key is not mapped to {@link StringValue}
      */
     default @Nullable String getStringOrNull(@NotNull Object key) {
-        return this.raw(key) instanceof StringValue value ? value.asString() : null;
+        return this.raw(key) instanceof StringRepresentable value ? value.asString() : null;
     }
 
     /**

core/src/test/java/com/github/siroshun09/configapi/core/node/MapNodeTest.java

@@ -184,6 +184,16 @@ protected Stream<NodeTestCase<MapNode>> nodeTestCases() {
                             assertSame(COMMENT, initial.getComment());
                             assertSame(COMMENT, view.getComment());
                         }
+                ),
+                nodeTest(
+                        "MapNode#getString(String)",
+                        MapNode.create(Map.of("a", "b", 1, 2)),
+                        node -> {
+                            assertEquals("b", node.getString("a"));
+                            assertEquals("2", node.getString(1));
+                            assertEquals("", node.getString("unknown"));
+                            assertEquals("default", node.getString("unknown", "default"));
+                        }
                 )
         );
     }