Bugfix: error when shift-clicking before ever clicking

diff --git a/AddonClearer.lua b/AddonClearer.lua
index c76171a..90c7db9 100644
--- a/AddonClearer.lua
+++ b/AddonClearer.lua
@@ -47,6 +47,7 @@ local firstControl = nil

 function AddonClearer:MultiSelect(button)
 	if not IsShiftKeyDown() then firstControl = self return false end
+	if firstControl == nil then firstControl = self return false end
 	if self ~= firstControl and IsShiftKeyDown() then
 		local firstRow = firstControl:GetParent().data
 		local currentRow = self:GetParent().data