[liquidbase]

Sorry for the late response.
The error occurs on line 89 if the character has no rested experience. Without (maxXP == 0) the script works as should. And the problem is not "nil" (my mistake in the interpretation) but it is a boolean instead of strings returned. With the expression the script throws the following error:

DuffedUI-8.0015\modules\misc\experience.lua:89: bad argument #4 to "format" (string expected, got boolean)
<in C code>
DuffedUI-8.0015\modules\misc\experience.lua:89: in function <DuffedUI\modules\misc\experience.lua:67>
 
Locals:
XP = 0
maxXP = 0
restXP = nil
percXP = true
(*temporary) = <function> defined =[C]:-1
(*temporary) = mouseFrame_Text {
 0 = <userdata>
}
IsMaxLevel = <function> defined @Interface\AddOns\DuffedUI\modules\misc\experience.lua:20
xpBar = Experience_xpBar {
 0 = <userdata>
 lockShow = 0
}
restedxpBar = Experience_restedxpBar {
 0 = <userdata>
 lockShow = 0
}
repBar = Experience_repBar {
 0 = <userdata>
 lockShow = 0
}
barHeight = 10
backdrop = Experience_Backdrop {
 0 = <userdata>
 backdrop = <unnamed> {
 }
}
Text = mouseFrame_Text {
 0 = <userdata>
}

Thanks for all help, you guys are great

Complete Script:

local D, C, L = unpack(select(2, ...))
 
local barHeight, barWidth = 10, 378
local font, fontsize, flags = C["media"].font, 11, "THINOUTLINE"
local barTex, flatTex = C["media"].normTex
local color = RAID_CLASS_COLORS[D.Class]
local FactionInfo = {
    [1] = {{ 170/255, 70/255,  70/255 }, "Hated", "FFaa4646"},
    [2] = {{ 170/255, 70/255,  70/255 }, "Hostile", "FFaa4646"},
    [3] = {{ 170/255, 70/255,  70/255 }, "Unfriendly", "FFaa4646"},
    [4] = {{ 200/255, 180/255, 100/255 }, "Neutral", "FFc8b464"},
    [5] = {{ 75/255,  175/255, 75/255 }, "Friendly", "FF4baf4b"},
    [6] = {{ 75/255,  175/255, 75/255 }, "Honored", "FF4baf4b"},
    [7] = {{ 75/255,  175/255, 75/255 }, "Revered", "FF4baf4b"},
    [8] = {{ 155/255,  255/255, 155/255 }, "Exalted","FF9bff9b"},
}
 
function colorize(r) return FactionInfo[r][3] end
 
local function IsMaxLevel()
    if UnitLevel("player") == MAX_PLAYER_LEVEL then
        return true
    end
end
 
local backdrop = CreateFrame("Frame", "Experience_Backdrop", UIParent)
backdrop:Size(barWidth, barHeight)
backdrop:SetPoint("BOTTOMLEFT", UIParent, "BOTTOMLEFT", 7, 178)
backdrop:SetBackdropColor(C["general"].backdropcolor)
backdrop:SetBackdropBorderColor(C["general"].backdropcolor)
backdrop:CreateBackdrop()
 
local xpBar = CreateFrame("StatusBar",  "Experience_xpBar", backdrop, "TextStatusBar")
xpBar:SetWidth(barWidth)
xpBar:SetHeight(GetWatchedFactionInfo() and (barHeight) or barHeight)
xpBar:SetPoint("TOP", backdrop,"TOP", 0, 0)
xpBar:SetStatusBarTexture(barTex)
if C["general"].classcolor then xpBar:SetStatusBarColor(color.r, color.g, color.b) else xpBar:SetStatusBarColor(31/255, 41/255, 130/255) end
 
local restedxpBar = CreateFrame("StatusBar", "Experience_restedxpBar", backdrop, "TextStatusBar")
restedxpBar:SetHeight(GetWatchedFactionInfo() and (barHeight) or barHeight)
restedxpBar:SetWidth(barWidth)
restedxpBar:SetPoint("TOP", backdrop, "TOP", 0, 0)
restedxpBar:SetStatusBarTexture(barTex)
restedxpBar:Hide()
 
local repBar = CreateFrame("StatusBar", "Experience_repBar", backdrop, "TextStatusBar")
repBar:SetWidth(barWidth)
repBar:SetHeight(IsMaxLevel() and barHeight - 0 or 0)
repBar:SetPoint("BOTTOM", backdrop, "BOTTOM", 0, 0)
repBar:SetStatusBarTexture(barTex)
 
local mouseFrame = CreateFrame("Frame", "Experience_mouseFrame", backdrop)
mouseFrame:SetAllPoints(backdrop)
mouseFrame:EnableMouse(true)
 
local Text = mouseFrame:CreateFontString("mouseFrame_Text", "OVERLAY")
Text:SetFont(font, fontsize, flags)
Text:SetPoint("CENTER", mouseFrame, "CENTER", 0, 0)
 
backdrop:SetFrameLevel(0)
restedxpBar:SetFrameLevel(1)
repBar:SetFrameLevel(2)
xpBar:SetFrameLevel(2)
mouseFrame:SetFrameLevel(3)
 
local function updateStatus()
    local XP, maxXP, restXP = UnitXP("player"), UnitXPMax("player"), GetXPExhaustion()
    local percXP = ((XP == 0) and (maxXP == 0)) or (math.floor((XP / maxXP) * 100))
 
    if IsMaxLevel() then
        xpBar:Hide()
        restedxpBar:Hide()
        repBar:SetHeight(barHeight)
        if not GetWatchedFactionInfo() then backdrop:Hide() else backdrop:Show() end
    else
        xpBar:SetMinMaxValues(min(0, XP), maxXP)
        xpBar:SetValue(XP)
 
        if restXP then
            Text:SetText(format("%s/%s (%s%%|cffb3e1ff+%d%%|r)", D.ShortValue(XP), D.ShortValue(maxXP), percXP, restXP / maxXP * 100))
            restedxpBar:Show()
            local r, g, b = color.r, color.g, color.b
            restedxpBar:SetStatusBarColor(r, g, b, .40)
            restedxpBar:SetMinMaxValues(min(0, XP), maxXP)
            restedxpBar:SetValue(XP + restXP)
        else
            restedxpBar:Hide()
            Text:SetText(format("%s/%s (%s%%)", D.ShortValue(XP), D.ShortValue(maxXP), percXP))
        end
 
        if GetWatchedFactionInfo() then
            xpBar:SetHeight(barHeight)
            restedxpBar:SetHeight(barHeight)
            repBar:SetHeight(2)
            repBar:Show()
        else
            xpBar:SetHeight(barHeight)
            restedxpBar:SetHeight(barHeight)
            repBar:Hide()
        end
    end
 
    if GetWatchedFactionInfo() then
        local name, rank, minRep, maxRep, value = GetWatchedFactionInfo()
        repBar:SetMinMaxValues(minRep, maxRep)
        repBar:SetValue(value)
        repBar:SetStatusBarColor(unpack(FactionInfo[rank][1]))
        Text:SetText(format("%d / %d (%d%%)", value - minRep, maxRep - minRep, (value - minRep) / (maxRep - minRep) * 100))
    end
 
    mouseFrame:SetScript("OnEnter", function()
        GameTooltip:SetOwner(mouseFrame, "ANCHOR_BOTTOMLEFT", -3, barHeight)
        GameTooltip:ClearLines()
        if not IsMaxLevel() then
            GameTooltip:AddLine("Experience:")
            GameTooltip:AddLine(string.format("XP: %s/%s (%d%%)", D.CommaValue(XP), D.CommaValue(maxXP), (XP / maxXP) * 100))
            GameTooltip:AddLine(string.format("Remaining: %s", D.CommaValue(maxXP - XP)))
            if restXP then GameTooltip:AddLine(string.format("|cffb3e1ffRested: %s (%d%%)", D.CommaValue(restXP), restXP / maxXP * 100)) end
        end
        if GetWatchedFactionInfo() then
            local name, rank, min, max, value = GetWatchedFactionInfo()
            if not IsMaxLevel() then GameTooltip:AddLine(" ") end
            GameTooltip:AddLine(string.format("Reputation: %s", name))
            GameTooltip:AddLine(string.format("Standing: |c"..colorize(rank) .. "%s|r", FactionInfo[rank][2]))
            GameTooltip:AddLine(string.format("Rep: %s/%s (%d%%)", D.CommaValue(value - min), D.CommaValue(max - min), (value - min)/(max - min) * 100))
            GameTooltip:AddLine(string.format("Remaining: %s", D.CommaValue(max - value)))
        end
        GameTooltip:Show()
    end)
    mouseFrame:SetScript("OnLeave", function() GameTooltip:Hide() end)
end
 
local frame = CreateFrame("Frame",nil,UIParent)
frame:RegisterEvent("PLAYER_LEVEL_UP")
frame:RegisterEvent("PLAYER_XP_UPDATE")
frame:RegisterEvent("UPDATE_EXHAUSTION")
frame:RegisterEvent("CHAT_MSG_COMBAT_FACTION_CHANGE")
frame:RegisterEvent("UPDATE_FACTION")
frame:RegisterEvent("PLAYER_ENTERING_WORLD")
frame:SetScript("OnEvent", updateStatus)