Merge pull request #306 from VH-Lab/306-add-heterogeneous-mixin-to-el…

…ement

Update element - Add Heterogeneous mixin and support 0-argument creation

+ndi/element.m

@@ -1,4 +1,4 @@
-classdef element < ndi.ido & ndi.epoch.epochset & ndi.documentservice
+classdef element < ndi.ido & ndi.epoch.epochset & ndi.documentservice & matlab.mixin.Heterogeneous
     % ndi.element - define or examine a element in the session
     %
     properties (GetAccess=public, SetAccess=protected)
@@ -29,6 +29,10 @@
             %
             set_identifier = 0;
 
+            if nargin == 0;
+                return % Support 0-argument construction
+            end
+
             needs_newdocument_call = 1;
 
             if numel(varargin)>=6,