fix isnull typo and formatting

docs/api/models/mixins/save-prepare-mixin.md

@@ -33,6 +33,25 @@ Translate columns into aliases (db names).
 
 `(Dict[str, str])`: dictionary of model that is about to be saved
 
+<a name="models.mixins.save_mixin.SavePrepareMixin._remove_not_ormar_fields"></a>
+#### \_remove\_not\_ormar\_fields
+
+```python
+ | @classmethod
+ | _remove_not_ormar_fields(cls, new_kwargs: dict) -> dict
+```
+
+Removes primary key for if it's nullable or autoincrement pk field,
+and it's set to None.
+
+**Arguments**:
+
+- `new_kwargs (Dict[str, str])`: dictionary of model that is about to be saved
+
+**Returns**:
+
+`(Dict[str, str])`: dictionary of model that is about to be saved
+
 <a name="models.mixins.save_mixin.SavePrepareMixin._remove_pk_from_kwargs"></a>
 #### \_remove\_pk\_from\_kwargs
 
@@ -52,6 +71,25 @@ and it's set to None.
 
 `(Dict[str, str])`: dictionary of model that is about to be saved
 
+<a name="models.mixins.save_mixin.SavePrepareMixin.parse_non_db_fields"></a>
+#### parse\_non\_db\_fields
+
+```python
+ | @classmethod
+ | parse_non_db_fields(cls, model_dict: Dict) -> Dict
+```
+
+Receives dictionary of model that is about to be saved and changes uuid fields
+to strings in bulk_update.
+
+**Arguments**:
+
+- `model_dict (Dict)`: dictionary of model that is about to be saved
+
+**Returns**:
+
+`(Dict)`: dictionary of model that is about to be saved
+
 <a name="models.mixins.save_mixin.SavePrepareMixin.substitute_models_with_pks"></a>
 #### substitute\_models\_with\_pks
 
@@ -110,3 +148,73 @@ fields with choices set to see if the value is allowed.
 
 `(Dict)`: dictionary of model that is about to be saved
 
+<a name="models.mixins.save_mixin.SavePrepareMixin._upsert_model"></a>
+#### \_upsert\_model
+
+```python
+ | @staticmethod
+ | async _upsert_model(instance: "Model", save_all: bool, previous_model: Optional["Model"], relation_field: Optional["ForeignKeyField"], update_count: int) -> int
+```
+
+Method updates given instance if:
+
+* instance is not saved or
+* instance have no pk or
+* save_all=True flag is set
+
+and instance is not __pk_only__.
+
+If relation leading to instance is a ManyToMany also the through model is saved
+
+**Arguments**:
+
+- `instance (Model)`: current model to upsert
+- `save_all (bool)`: flag if all models should be saved or only not saved ones
+- `relation_field (Optional[ForeignKeyField])`: field with relation
+- `previous_model (Model)`: previous model from which method came
+- `update_count (int)`: no of updated models
+
+**Returns**:
+
+`(int)`: no of updated models
+
+<a name="models.mixins.save_mixin.SavePrepareMixin._upsert_through_model"></a>
+#### \_upsert\_through\_model
+
+```python
+ | @staticmethod
+ | async _upsert_through_model(instance: "Model", previous_model: "Model", relation_field: "ForeignKeyField") -> None
+```
+
+Upsert through model for m2m relation.
+
+**Arguments**:
+
+- `instance (Model)`: current model to upsert
+- `relation_field (Optional[ForeignKeyField])`: field with relation
+- `previous_model (Model)`: previous model from which method came
+
+<a name="models.mixins.save_mixin.SavePrepareMixin._update_relation_list"></a>
+#### \_update\_relation\_list
+
+```python
+ | async _update_relation_list(fields_list: Collection["ForeignKeyField"], follow: bool, save_all: bool, relation_map: Dict, update_count: int) -> int
+```
+
+Internal method used in save_related to follow deeper from
+related models and update numbers of updated related instances.
+
+**Arguments**:
+
+- `fields_list (Collection["ForeignKeyField"])`: list of ormar fields to follow and save
+- `relation_map (Dict)`: map of relations to follow
+- `follow (bool)`: flag to trigger deep save -
+by default only directly related models are saved
+with follow=True also related models of related models are saved
+- `update_count (int)`: internal parameter for recursive calls -
+number of updated instances
+
+**Returns**:
+
+`(int)`: tuple of update count and visited
+