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copied!<p>Null just means null. There's no inherent security issue there.</p> <p>As a web service is a public API, you should be rigorously checking all input data and expect badly-formed input to occur. You can never assume that the client code does the right thing and doesn't send you null either (maliciously or otherwise). </p> <p>So Empty strings or other sentinel values don't save you from checking input, and they don't necessarily make life easier either. Semantically empty strings aren't null either, they're empty.</p> <p>For what it's worth, the xml generated by the .net SoapFormatter for a null is plain old nothing, and that's not the same as an empty string. It's a trivial example, but informative. If you send null you're also sending less data, which may be something to consider.</p> <pre><code>{ [WebMethod] public MyClass HelloWorld() { MyClass val = new MyClass() { IsValid = false, HelloString = "Hello World", BlankString = "", Nested = new NestedClass { Name = "Bob" } }; return val; } } public class MyClass { public bool IsValid { get; set; } public string HelloString { get; set; } public string BlankString { get; set; } public string OtherString { get; set; } public NestedClass Nested { get; set; } public NestedClass NullNested { get; set; } } public class NestedClass { public string Name { get; set; } } </code></pre> <p>yields the following xml response. Note how <code>OtherString</code> and <code>NullNested</code> are missing entirely from the response, which is different to <code>BlankString</code>.</p> <pre><code><MyClass> <IsValid>false</IsValid> <HelloString>Hello World</HelloString> <BlankString /> <Nested> <Name>Bob</Name> </Nested> </MyClass> </code></pre>

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