How to add programatically a RichtText field to a contenttype

Question

THe following code throws me an exception, System.ArgumentNullException: Key cannot be null. Parameter name: key at System.Collections.Hashtable.get_Item(Object key) at Microsoft.SharePoint.SPFieldLinkCollection.Exists(String name, SPFieldLink& fldFound)

also here: but nobody answered. http://social.technet.microsoft.com/Forums/sk/sharepoint2010programming/thread/5618e800-c4b5-4308-a5d8-c509aabb120e

My code is as follows:

using (SPSite spsite = new SPSite(strurl))
                {
                    using (SPWeb currentWeb = spsite.OpenWeb())
                    {
                        try
                        {
                            currentWeb.AllowUnsafeUpdates = true;
                            SPContentType agendaPointsProposedCT = currentWeb.ContentTypes[Meetings.Common.Constants.CONTENTTYPES_AGENDAPOINTPROPOSED_NAME];
                            SPField reasonReturnedField = CreateHtmlField(currentWeb, Meetings.Common.Constants.FIELDS_AGENDAPOINTSREASONRETURNED_NAME);
                            //SPField reasonReturnedField = currentWeb.Fields.GetFieldByInternalName(reasonReturnedFieldName);

                            reasonReturnedField.Group = "$Resources:SPNLXXX,Field_XXXColumns_Group";                           
                            string schemaXmlWithResourceTokens = reasonReturnedField.SchemaXmlWithResourceTokens;
                            string displaynamelocalized = "$Resources:SPNLXXX,Field_ReasonReturned_Name";
                            string returnValue;
                            int indexOfAttributeName = schemaXmlWithResourceTokens.IndexOf("DisplayName", StringComparison.InvariantCultureIgnoreCase);
                            int indexOfAttibuteValueBegin = schemaXmlWithResourceTokens.IndexOf('"', indexOfAttributeName);
                            int indexOfAttributeValueEnd = schemaXmlWithResourceTokens.IndexOf('"', indexOfAttibuteValueBegin + 1);
                            returnValue = schemaXmlWithResourceTokens.Substring(0, indexOfAttibuteValueBegin + 1) + displaynamelocalized + schemaXmlWithResourceTokens.Substring(indexOfAttributeValueEnd);
                            reasonReturnedField.SchemaXml = returnValue;
                            //reasonReturnedField.Update();

                            SPFieldLink fieldLink = new SPFieldLink(currentWeb.AvailableFields.GetField(reasonReturnedField.InternalName));
                            //Check if the Field reference exists
                            if (!agendaPointsProposedCT.Fields.ContainsField(reasonReturnedField.Title))
                            {
                                agendaPointsProposedCT.FieldLinks.Add(fieldLink);
                                agendaPointsProposedCT.Update(true);
                            }
                            MoveFieldInColumnOrderToLastPosition(currentWeb, Meetings.Common.Constants.CONTENTTYPES_AGENDAPOINTPROPOSED_NAME, reasonReturnedField.InternalName);
                        }
                        catch (Exception ex)
                        {
                            Logger.LogError("XXX", "AddReasonReturnedFieldsToContentTypeAgendaPointProposed(SPListItem item, SPWeb elevatedTargetWeb)", ex);
                            throw;
                        }
                        finally
                        {
                            currentWeb.AllowUnsafeUpdates = false;
                        }
                    }
                } 


private static HtmlField CreateHtmlField(SPWeb currentWeb, string fieldName)
        {
            HtmlField fieldHtml;
            fieldName = fieldName.Trim();
            SPFieldCollection spFieldCollection = currentWeb.Fields;
            if (currentWeb.AvailableFields.ContainsFieldWithStaticName(fieldName))
            {
                fieldHtml = (HtmlField)spFieldCollection[fieldName];
            }
            else
            {
                fieldHtml = new HtmlField(spFieldCollection, "HTML", fieldName)
                {
                    Title = fieldName,
                    Group = "$XXX,Field_XXXColumns_Group",
                    ShowInEditForm = true,
                    StaticName = fieldName,
                    RichText = true,
                    RichTextMode = SPRichTextMode.FullHtml,
                    AllowHyperlink = true,
                    AllowDeletion = true
                };
                spFieldCollection.Add(fieldHtml);            
            }
            return fieldHtml;
        }

Answer 1

Check that your reasonReturnedField.Title and fieldName are not null.

I can not see on MSDN that is is suppose to throw any exception, not even by inherited classes. But by disassembling SPFieldCollection I see it calls this.DisplayNameDict.ContainsKey((object) fieldName) which is Dictionary that according to MSDN (ContainsKey) will throw the exception you reference.

Answer 2

Finally, I was able to solve it:

Solution I found is here: http://levalencia.wordpress.com/2012/09/17/add-spfieldmultilinetext-html-field-by-code-wont-show-html-ribbon-tools/