casting bar: attempt to perform arithmetic

[ObbleYeah]

\castbar.lua:77: attempt to perform arithmetic on local "endTime" (a nil value)

happens when i'm casting and my target is channeling simultaneously.

--
 
-- latency ------------------------------------------------------------------------------
 
    local function findCastLatency(self)
        local latency = self.latency
        local width = self:GetWidth()
        local _, _, _, ms = GetNetStats()
 
        if (ms~=0) then
            local safeZonePercent = (width/self.max) * (ms/1e5)
            if(safeZonePercent > 1) then
                safeZonePercent = 1
            end
            latency:SetWidth(width*safeZonePercent)
            latency:Show()
        else
            latency:Hide()
        end
    end
 
    local function cbLatency(self, event, ...)   
        local name, _, text, texture, startTime, endTime, castid, interrupt         
        local unit, spellName, _, id, spellId = ...
        local cb = self.latency     
        
        -- we don't want to look at any castbars but our own
        if (self.unit~="player") then return end
    
        if (event=="UNIT_SPELLCAST_START") then 
            if (cb) then
                name, _, text, texture, startTime, endTime, _, castid, interrupt = UnitCastingInfo(self.unit)
                endTime = endTime / 1e3
                startTime = startTime / 1e3
                local max = endTime - startTime
                self.max = max 
                cb:ClearAllPoints()
                cb:SetPoint("TOP")
                cb:SetPoint("BOTTOM")
                cb:SetPoint("RIGHT")
            end            
            findCastLatency(self)
        elseif (event=="UNIT_SPELLCAST_CHANNEL_START") then
            if (cb) then
                name, _, text, texture, startTime, endTime, _, castid, interrupt = UnitChannelInfo(self.unit)
                endTime = endTime / 1e3
                startTime = startTime / 1e3
                local max = endTime - startTime
                self.max = max 
                self.casting = nil
                self.castid = nil
                cb:ClearAllPoints()
                cb:SetPoint("TOP")
                cb:SetPoint("BOTTOM")
                cb:SetPoint("LEFT")
            end            
            findCastLatency(self)
        elseif ((event=="UNIT_SPELLCAST_STOP") or (event=="UNIT_SPELLCAST_CHANNEL_STOP") or  (event=="UNIT_SPELLCAST_FAILED") or (event=="UNIT_SPELLCAST_INTERRUPTED")) then
            if (not self.casting and not self.channeling) then
                cb:Hide()
                self.queuezone:Hide()
            end
        end
    end
      
    hooksecurefunc("CastingBarFrame_OnEvent", cbLatency)

line 77 is the UnitChannelInfo endTime. What's causing this?