how to assign empty string for non existence of the XML path. getting error since path is not available

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Hi friends,
i am trying to create a list of object from XMl
problem is, in some cases particular path is not available. so my code throwing an exception stating "Object reference not set to an instance of object". How can i overcome this situation. if particular node is not available value should be empty.
please see the inline comments

C#

public static List<GetFaNumInBranch> SearchByUserID(string xmlstring, string UserId)
{
List<GetFaNumInBranch> FaDetails_Filter = new List<GetFaNumInBranch>();
XElement Xele;
Xele = RemoveAllNamespaces(XElement.Parse(xmlstring));
UserId = "PE9603";
var FaDetails_Filters = Xele.Descendants("FaNumInBranch")
	  .Where(item =>
	  {
		  string BranchUserId = (string)item.Element("BranchUserId") ?? "";
		  return BranchUserId != null && BranchUserId == UserId;
	  })
	 .Select(item => new GetFaNumInBranch
	 { 
		 FaType = (string)item.Element("AlternateFALIST").Element("AlternateFA").Element("FaType") ?? "",// in some case specific path will not available.so i am getting object reference  error
		 PrimaryFANumber = (string)item.Element("PrimaryFANumber") ?? "",
		 PrimaryBranch = (string)item.Element("PrimaryBranch") ?? "",
		 FirstName = (string)item.Element("FirstName") ?? "",
		 LastName = (string)item.Element("LastName") ?? "",
		 EmpNum = (string)item.Element("EmpNum") ?? "",
		 BranchUserId = (string)item.Element("BranchUserId") ?? ""
	 })
	 .ToList();               
return FaDetails_Filter;
}

XML

<FaNumInBranch>
  <BranchUserId>PB6442</BranchUserId>
  <EmpNum>B6442</EmpNum>
  <LastName>YAMADA </LastName>
  <FirstName>KAY </FirstName>
  <PrimaryBranch>0237</PrimaryBranch>
  <PrimaryFANumber>0663</PrimaryFANumber>
  <AlternateFALIST>
    <AlternateFA>
      <FaType>S</FaType>
      <BranchFAList>
        <BranchFA>
          <Branch>0237</Branch>
          <FA>0676</FA>
        </BranchFA>

Posted 22-Sep-15 20:44pm

jinesh sam

Updated 22-Sep-15 20:47pm

v3

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Matt T Heffron · Answer 1 · 2015-09-25T13:46:00

In C# 6 it would be easy with the new ?. operator:

C#

FaType = (string)item.Element("AlternateFALIST")?.Element("AlternateFA")?.Element("FaType") ?? ""

Otherwise, I'd suggest using a separate (or anonymous or lambda) method to walk to the FAType:

C#

private static XElement SafePathWalker(XElement start, params string[] elementNames)
{
  // should check for start and elementNames != null
  XElement result = start;
  foreach (string name in elementNames)
  {
    result = result.Element(name);
    if (result == null)
      return null;
  }
  return result;  
}

Then:

C#

FaType = (string)SafePathWalker(item, "AlternateFALIST", "AlternateFA", "FAType") ?? ""

Edit: MTH
The SafePathWalker could be put into an extension methods class:

C#

public static ExtensionMethods
{
  public static XElement SafePathWalker(this XElement start, params string[] elementNames)
  {
    // should check for elementNames != null
    XElement result = start;
    // A regular for loop could work also (compare with above)
    for (int i = 0; result != null && i < elementNames.Length; ++i)
    {
      result = result.Element(elementNames[i]);
    }
    return result;  
  }
}

Then:

C#

FaType = (string)item.SafePathWalker("AlternateFALIST", "AlternateFA", "FAType") ?? ""