<!DOCTYPE qhelp PUBLIC

"-//Semmle//qhelp//EN"

"qhelp.dtd">

<qhelp>

<overview>

<p>If a variable is dereferenced, for example as the qualifier in a method call, and the

variable may have a <code>null</code> value on some execution paths leading to the

dereferencing, the dereferencing may result in a <code>NullReferenceException</code>.

</p>

</overview>

<recommendation>

<p>Ensure that the variable does not have a <code>null</code> value when it is dereferenced.

</p>

</recommendation>

<example>

<p>

In the following example, the method <code>DoPrint()</code> dereferences its parameter

<code>o</code> unconditionally, resulting in a <code>NullReferenceException</code> via

the call <code>DoPrint(null)</code>.

</p>

<sample src="NullMaybeBad.cs" />

<p>

In the revised example, the method <code>DoPrint()</code> guards the dereferencing with

a <code>null</code> check.

</p>

<sample src="NullMaybeGood.cs" />

</example>

<references>

<li>Microsoft, <a href="https://docs.microsoft.com/en-us/dotnet/api/system.nullreferenceexception">NullReferenceException Class</a>.</li>

</references>

</qhelp>