# Expressions

> The Logic configuration editor enables you to build expressions using logic blocks. You can drag and drop the available Logic blocks from the side panel to the Logic configuration canvas.

The Logic configuration editor enables you to build expressions using logic blocks. You can drag and drop the available Logic blocks from the side panel to the Logic configuration canvas.

You can use the Expand all and Collapse all icons to view or hide all the available Logic blocks. The Search function enables you to quickly search for a Logic block.

When you select a component on the canvas, you can define the parameters for the component.

## NULL values

`NULL` means that a data value does not exist in the data or that the value is unknown.

For example, if you have a source table for `Customers`, and some customers did not provide a phone number, the `Phone_number` field for those customers will be marked as `NULL`.

Calculations involving `NULL` values will themselves yield a `NULL` value. For example `7 + NULL = NULL`, because the value of `NULL` is unknown, there is no way to add seven to nothing.

:::note
`NULL` is not the same as zero (0), or an empty value (""). Zero (0) is a number, and an empty value is a value with no characters. `NULL` represents the absence of a value altogether. You can use the [Compare](https://docs.uipath.com/process-mining/automation-cloud/latest/user-guide/comparefunctions#compare) functions `IS NULL` and `IS NOT NULL` to check whether the value of a field or expression is `NULL` or not `NULL`.
:::

## Example field: Needs review

The following illustration shows an example of nested `IF - THEN - ELSE` statements and an `AND` comparison.

![docs image](https://dev-assets.cms.uipath.com/assets/images/process-mining/process-mining-docs-image-542857-a0144b62-ae21f281.webp)

This example creates a new `Needs review` field in the `Cases` table**.** This field defines the cases that have a value more than 100,000 that you want to have reviewed by a partner.

* The first `IF - THEN - ELSE` function checks if `Case status` is `Open`. If the condition returns `true` the case is set to `In progress`. If the condition returns `false` , the `ELSE` argument is executed.
* The second `IF - THEN - ELSE` function checks if the `Case type` is `Partner` and the `Case value` is more than 100,000 using an `AND` comparison. If the `AND` comparison returns `true`, the case is set to `Review Required`. If the `AND` comparison returns `false`, the `ELSE` argument is executed which sets the case to `Review Not Required`.

The following illustration shows an example result of the logic configuration.

![Example results for the Needs review field logic configuration](https://dev-assets.cms.uipath.com/assets/images/process-mining/process-mining-example-results-for-the-needs-review-field-logic-configuration-542863-7a66f90d-55905f02.webp)