关于c＃：检查string是否为null

Check if string is null

我想检查我的变量(crphoto1)是否为空。如果crphoto1为空，crphoto1数据应为空；如果crphoto1不为空，crphoto1数据应类似于此字节[]crphoto1数据=file.readAllBytes(crphoto1)；。下面的代码给了我错误，我如何修复它？

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if (string.IsNullOrEmpty(crphoto1))
{
string crPhoto1Data ="";
}
else
{
byte[] crPhoto1Data = File.ReadAllBytes(crphoto1);
}

var ph1link ="http://" + ipaddress + Constants.requestUrl +"Host=" + host +"&Database=" + database +"&Contact=" + contact +"&Request=tWyd43";
string ph1contentType ="application/json";
JObject ph1json = new JObject
{
{"ContactID", crcontactID },
{"Photo1", crPhoto1Data }
};