The given key was not present in the dictionary - plugins

Question

I am developing a plugin in crm 5.0 to retrieve date "ct_valuedate" from an entity called "ct_marketvalue" and formatting and saving in a field called "ct_dateserial"
I get an error while I debug "The given key was not present in the dictionary"
public class MarketValueDateFormatting : PluginBase
{
protected override void ExecutePlugin()
{
try
{
switch (_crmMessage)
{
case CrmPluginMessageEnum.Create:
if (_context.InputParameters.Contains("ct_marketvalue"))
{
//Obtain the logical name of the entity
string moniker1 = ((EntityReference)_context.InputParameters["EntityMoniker"]).LogicalName;
//Verify that the target entity represents an Account.
//If not, this plug-in was not registered correctly.
if (moniker1.Equals("ct_marketvalue"))
{
Entity marketvalueimage = (Entity)_context.PostEntityImages["ct_marketvalue"];
Guid marketvalueid = marketvalueimage.Id;
if (marketvalueimage.Contains("ct_valuedate"))
{
DateTime dateserial = (DateTime)marketvalueimage.Attributes["ct_valuedate"];
String dateserialstring = dateserial.ToString("YYYYMMdd");
Ct_marketvalue marketvalue = new Ct_marketvalue();
marketvalue.Ct_dateserial = dateserialstring;
marketvalue.Id = marketvalueid;
_serviceContext.UpdateObject(marketvalue);
}
}
}
break;
}
catch (Exception ex)
{
throw ex;
}
}
}
}

Answer 1

Few notes about your code.
You should check in your code that _context.PostEntityImages contains "ct_marketvalue". It's possible either to forgot register or to do a mistake in image name.
Might be better use .ToEntity rather than access attributes using .Attributes["ct_valuedate"].
I'm not sure what is purpose of the plugin you wrote, but it looks it is post stage plugin and it updates the same entity instance, that was in InputParameters. Might be better to make this plugin pre stage and update value directly in InputParameters. Because, if not "The given key was not present in the dictionary" exception, it will cause infinite loop. You will need check context.Depth.