fix isnull typo and formatting

docs/api/models/traversible.md

@@ -0,0 +1,78 @@
+<a name="models.traversible"></a>
+# models.traversible
+
+<a name="models.traversible.NodeList"></a>
+## NodeList Objects
+
+```python
+class NodeList()
+```
+
+Helper class that helps with iterating nested models
+
+<a name="models.traversible.NodeList.add"></a>
+#### add
+
+```python
+ | add(node_class: Type["RelationMixin"], relation_name: str = None, parent_node: "Node" = None) -> "Node"
+```
+
+Adds new Node or returns the existing one
+
+**Arguments**:
+
+- `node_class (ormar.models.metaclass.ModelMetaclass)`: Model in current node
+- `relation_name (str)`: name of the current relation
+- `parent_node (Optional[Node])`: parent node
+
+**Returns**:
+
+`(Node)`: returns new or already existing node
+
+<a name="models.traversible.NodeList.find"></a>
+#### find
+
+```python
+ | find(node_class: Type["RelationMixin"], relation_name: Optional[str] = None, parent_node: "Node" = None) -> Optional["Node"]
+```
+
+Searches for existing node with given parameters
+
+**Arguments**:
+
+- `node_class (ormar.models.metaclass.ModelMetaclass)`: Model in current node
+- `relation_name (str)`: name of the current relation
+- `parent_node (Optional[Node])`: parent node
+
+**Returns**:
+
+`(Optional[Node])`: returns already existing node or None
+
+<a name="models.traversible.Node"></a>
+## Node Objects
+
+```python
+class Node()
+```
+
+<a name="models.traversible.Node.visited"></a>
+#### visited
+
+```python
+ | visited(relation_name: str) -> bool
+```
+
+Checks if given relation was already visited.
+
+Relation was visited if it's name is in current node children.
+
+Relation was visited if one of the parent node had the same Model class
+
+**Arguments**:
+
+- `relation_name (str)`: name of relation
+
+**Returns**:
+
+`(bool)`: result of the check
+