Node.placeNodeIn(): add node to tree under the path of named elements

Any intervening nodes that don't exist will be created.

e.g. placeNodeIn(node, "alpha", "beta")

Will add node:

[root]
    "alpha"
        "beta"
            node

src/main/java/net/kemitix/node/Node.java

@@ -127,6 +127,14 @@ public interface Node<T> {
     Optional<Node<T>> walkTree(final List<T> path);
 
     /**
+     * Places the node in the tree under by the path. Intervening empty
+     * nodes are created as needed.
+     *
+     * @param node the node to place
+     * @param path the path to contain the new node
+     */
+    void placeNodeIn(Node<T> node, String... path);
+
     /**
      * Searches for a child with the name given.
      *

src/main/java/net/kemitix/node/NodeItem.java

@@ -1,5 +1,6 @@
 package net.kemitix.node;
 
+import java.util.Arrays;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Optional;
@@ -325,6 +326,46 @@ public class NodeItem<T> implements Node<T> {
         }
     }
 
+    @Override
+    public void placeNodeIn(final Node<T> nodeItem, final String... path) {
+        if (path.length == 0) {
+            if (nodeItem.isNamed()) {
+                final Optional<Node<T>> childNamed = findChildNamed(
+                        nodeItem.getName());
+                if (childNamed.isPresent()) {
+                    final Node<T> existing = childNamed.get();
+                    if (!existing.isEmpty()) {
+                        throw new NodeException(
+                                "A non-empty node with that name already "
+                                        + "exists here");
+                    } else {
+                        existing.getChildren().forEach(nodeItem::addChild);
+                        existing.removeParent();
+                        nodeItem.setParent(this);
+                        return;
+                    }
+                }
+            }
+            addChild(nodeItem);
+            return;
+        }
+        String item = path[0];
+        final Optional<Node<T>> childNamed = findChildNamed(item);
+        Node<T> child;
+        if (!childNamed.isPresent()) {
+            child = new NodeItem<>(null, item, this);
+        } else {
+            child = childNamed.get();
+            if (child.isEmpty()) {
+                if (path.length == 1) {
+                    getChildren().forEach(nodeItem::addChild);
+                    nodeItem.setParent(this);
+                }
+            }
+        }
+        child.placeNodeIn(nodeItem, Arrays.copyOfRange(path, 1, path.length));
+    }
+
     @Override
     public String drawTree(final int depth) {
         final StringBuilder sb = new StringBuilder();