add TCN#setIfAbsent

src/main/java/de/tudbut/parsing/TCN.java

@@ -63,6 +63,22 @@ public class TCN {
         map.set(key, o);
     }
     
+    /**
+     * Sets something in the map if it doesn't exist
+     * @param key Key
+     * @param o Object, can be a native type, string, or another TCN (or TCNArray)
+     */
+    public void setIfAbsent(String key, Object o) {
+        /*TLMap<String, Object> map = this.map;
+        ArrayList<String> path = new ArrayList<>(Arrays.asList(key.split("#")));
+
+        while (path.size() > 1) {
+            map = ((TCN) map.get(path.remove(0))).map;
+        }
+         */
+        map.setIfNull(key, o);
+    }
+
     public String getString(String key) {
         Object o = map.get(key);
         if(o != null)