# Math Tags Null Value Error: Ending Position Out of Bounds (22) Stack Invalid Double

This error usually means a field inside a `<MATH>` tag is blank.

S-Docs expects a number.

If a merge field returns `null` instead, the calculation can fail with errors like:

* `Ending position out of bounds: 22 STACK`
* `Invalid double`

### Fix 1: Replace blank values with `0`

This is the fastest fix.

Add `replaceall=" ,0"` to any numeric field that might be blank.

{% code title="null-safe-math.xml" %}

```xml
<MATH>
  {{!Opportunity.Amount replaceall=" ,0"}} +
  {{!Opportunity.CustomField__c replaceall=" ,0"}}
</MATH>
```

{% endcode %}

Use this pattern when:

* the field is numeric
* blank values should behave like zero
* you want the calculation to always run

### Fix 2: Only run math when data exists

Use a named query and conditional logic when a missing value means the calculation should not run at all.

This pattern first checks whether matching records exist.

Then it runs the calculation only when there is data to use.

{% code title="conditional-math-with-named-queries.xml" %}

```xml
<!--{{!<LineItemsSOQL>
<class>none</class>
<queryname>myQuery1</queryname>
<soql>
SELECT count(ID) cid
FROM Opportunity
WHERE AccountId = '{{!Account.ID}}'
</soql>
</LineItemsSOQL>}}-->

<!--{{!<LineItemsSOQL>
<class>none</class>
<queryname>myQuery2</queryname>
<soql>
SELECT SUM(Amount) total, SUM(CustomField__c) reduce
FROM Opportunity
WHERE AccountId = '{{!Account.ID}}'
</soql>
</LineItemsSOQL>}}-->

<!--RENDER='{{!myQuery1.cid}} > 0' -->
<MATH>{{!myQuery2.total}} + {{!myQuery2.reduce}}</MATH>
<!--ENDRENDER-->
```

{% endcode %}

Use this pattern when:

* the calculation depends on query results
* zero would be misleading
* you only want output when records exist

{% hint style="info" %}
This issue is commonly tied to the `Invalid double` error. If you see both messages, check for blank numeric fields first.
{% endhint %}

### Quick checklist

Before you test again, confirm these items:

* every field inside `<MATH>` returns a number
* blank numeric fields use `replaceall=" ,0"` when needed
* query-based math is wrapped in `RENDER` when results may be missing
* your `<MATH>` tag opens and closes correctly

### Next step

For a beginner walkthrough, see [Get Started with Calculations](broken://spaces/WKNnJmhJBQwhdk5WBFsi/pages/AWClXpysUyYPXaqZa7po).


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