//create comment block and get the block that summoned the context menu
     var comment = workspace.newBlock('ta_comment');
     var block = Blockly.ContextMenu.currentBlock;

     //connect up comment block
     comment.previousConnection.connect(block.previousConnection.targetConnection);
     comment.nextConnection.connect(block.previousConnection);

     //init
     comment.initSvg();

     //render updated workspace
     workspace.render();

Hi you need is just override the getMatchingConnection function from blockly and comment the check in the function

window.Blockly.Block.prototype.getMatchingConnection = function(otherBlock, conn) {
  var connections = this.getConnections_(true);
  var otherConnections = otherBlock.getConnections_(true);
  // if (connections.length !== otherConnections.length) {
  //   throw Error("Connection lists did not match in length.");
  // }
  for (var i = 0; i < otherConnections.length; i++) {
    if (otherConnections[i] === conn) {
      return connections[i];
    }
  }
  return null;
};