<!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 has a <code>null</code> value on all possible execution paths leading to the

dereferencing, the dereferencing is guaranteed to 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 examples, the condition <code>s.Length > 0</code> is only

executed if <code>s</code> is <code>null</code>.

</p>

<sample src="NullAlwaysBad.cs" />

<p>

In the revised example, the condition is guarded correctly by using <code>&amp;&amp;</code> instead of

<code>||</code>.

</p>

<sample src="NullAlwaysGood.cs" />

</example>

<references>

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

</references>

</qhelp>