When adding taxonomy values via CSOM Exception "Value cannot be null. ParamterName:termId" thrown

Question

I am trying to set the value of a Sharepoint 2013 TaxonomyField in CSOM but when I execute the last context.ExecuteQuery(), after taxField.Update(), a exception is thrown that reads `A first chance exception of type 'Microsoft.SharePoint.Client.ServerException' occurred in Microsoft.SharePoint.Client.Runtime.dll Additional information: Value cannot be null. Parameter name: termId'. Everything loads fine, it finds the term and I'm out of ideas.

        public void AddTaxonomyFieldValue(ClientContext context, ListItem item, string destinationColumn, IEnumerable<string> terms, Guid termGroupId, Guid termSetId, int lcid)
    {
        var taxonomySession = TaxonomySession.GetTaxonomySession(context);
        var store = taxonomySession.TermStores.GetByName("Managed Metadata Service2");
        var group = store.GetGroup(termGroupId);
        var set = group.TermSets.GetById(termSetId);
        var existingTerms = set.GetAllTerms();
        var field = item.ParentList.Fields.GetByInternalNameOrTitle(destinationColumn);
        var taxField = context.CastTo<TaxonomyField>(field);
        context.Load(existingTerms, et => et.Include(t => t.Labels.Include(l => l.Value, l => l.Language), t => t.Id, t=> t.PathOfTerm, t => t));
        context.ExecuteQuery();

        var fieldTermValues = new Collection<Term>();

        foreach (var term in terms)
        {
            var lmi = new LabelMatchInformation(context);
            lmi.TermLabel = term;
            // Find existing term
            var existingTerm =
                existingTerms.FirstOrDefault(t => t.Labels.Any(l => l.Language == lcid && l.Value == term));

            if (null == existingTerm)
            {
                // create new term
                existingTerm = set.CreateTerm(term, lcid, new Guid());
                set.TermStore.CommitAll();
                context.Load(existingTerm);
                context.ExecuteQuery();
            }

            fieldTermValues.Add(existingTerm);
        }
        // set taxonomy field
        taxField.SetFieldValueByCollection(item, fieldTermValues, lcid);
        taxField.Update();
        // Exception Thrown Here
        context.ExecuteQuery();
    }

EDIT 1: I just noticed that the taxonomy term I created in that foreach loop has a Unique Identifier == "00000000-0000-0000-0000-000000000000" when looking at it from the Sharepoint site. So I'm thinking my problem lies there.

Answer 1

I figured out my problem and it was due to a bad invalid term id being created.

In the following code

// crete new term
existingTerm = set.CreateTerm(term, lcid, new Guid());

I should be doing

existingTerm = set.CreateTerm(term, lcid, Guid.NewGuid());