Update incremental-models.md (#5306)

If event_time is NULL or the table is truncated, the condition will
always be true and load all records. This is an edge case.

If a final table is truncated it will return the NULL as the result 

( select * from table where event_time > NULL ) --> return no results 

It will not have any data in it and dbt considers it as incremental
load. then the model will fail, to avoid that situation. In dbt we don't
have anything to handle this situation.

## What are you changing in this pull request and why?
<!---
Describe your changes and why you're making them. If related to an open 
issue or a pull request on dbt Core, then link to them here! 

To learn more about the writing conventions used in the dbt Labs docs,
see the [Content style
guide](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/content-style-guide.md).
-->

## Checklist
<!--
Uncomment when publishing docs for a prerelease version of dbt:
- [ ] Add versioning components, as described in [Versioning
Docs](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/single-sourcing-content.md#versioning-entire-pages)
- [ ] Add a note to the prerelease version [Migration
Guide](https://github.com/dbt-labs/docs.getdbt.com/tree/current/website/docs/docs/dbt-versions/core-upgrade)
-->
- [ ] Review the [Content style
guide](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/content-style-guide.md)
so my content adheres to these guidelines.
- [ ] For [docs
versioning](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/single-sourcing-content.md#about-versioning),
review how to [version a whole
page](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/single-sourcing-content.md#adding-a-new-version)
and [version a block of
content](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/single-sourcing-content.md#versioning-blocks-of-content).
- [ ] Add a checklist item for anything that needs to happen before this
PR is merged, such as "needs technical review" or "change base branch."

Adding or removing pages (delete if not applicable):
- [ ] Add/remove page in `website/sidebars.js`
- [ ] Provide a unique filename for new pages
- [ ] Add an entry for deleted pages in `website/vercel.json`
- [ ] Run link testing locally with `npm run build` to update the links
that point to deleted pages

---------

Co-authored-by: Mirna Wong <[email protected]>

website/docs/docs/build/incremental-models.md

@@ -70,7 +70,8 @@ from {{ ref('app_data_events') }}
 
   -- this filter will only be applied on an incremental run
   -- (uses >= to include records whose timestamp occurred since the last run of this model)
-  where event_time >= (select coalesce(max(event_time), '1900-01-01') from {{ this }})
+  -- (If event_time is NULL or the table is truncated, the condition will always be true and load all records)
+where event_time >= (select coalesce(max(event_time),'1900-01-01'::TIMESTAMP) from {{ this }} )
 
 {% endif %}
 ```