This code:
XmlNode columnNode = null;
columnNode = xmlDoc.CreateElement("SYSID");
columnNode.InnerText = ""; // Empty string
newRowNode.AppendChild(columnNode);
...does this:
<SYSID>
</SYSID>
And I would like to have this, when string is empty:
<SYSID></SYSID>
Is there any solution?
If you have another tool that requires that format, then the other tool is wrong - it is incapable of reading XML. So if you have control over the other tool, I'd suggest fixing it rather than trying to coerce your code into matching it.
If you can't fix the other tool...
If you're just building a Document to write it out to disk, then you can use a stream and write the elements directly yourself (as simple text). This will be faster (and may well be easier) than using an XmlDoc.
As an improvement on that, you may be able to use an XmlWriter to write elements, but when you go to write an empty element, write raw text to the stream (i.e. writer.WriteRaw("<SYSID></SYSID>\n")) so that you control the formatting for those particular elements.
If you need to build an in-memory XmlDocument, then to a large extent you have to put up with the formatting that it uses when you ask it to serialize to disk (aside from basic settings like PreserveWhitespace, you're asking the document to deal with storing the information, and so you lose a lot of control over the functionality that the XmlDocument encapsulates). THe best suggestion I can think of in this case would be to write the XmlDocument to a MemoryStream and then post-process that memory stream to remove newlines from within empty elements. (Yuck!)