While browsing the AH
Edit 1:
Happened over the Cinder Pup pet, tooltip now missing for that pet and only that pet, other pets showing as normal.
Edit 2:
Hm, also affected the Lost Netherpup pet.

Date: 2015-08-21 11:32:49
ID: 1
Error occured in: Global
Count: 1
Message: ..\AddOns\BetterBattlePetTooltip\Core.lua line 152:
bad argument #1 to 'gsub' (string expected, got nil)
Debug:

BetterBattlePetTooltip\Core.lua:152: GetOwnedBattlePetString()
..\FrameXML\BattlePetTooltip.lua:22:
..\FrameXML\BattlePetTooltip.lua:3

...ace\AddOns\Blizzard_AuctionUI\Blizzard_AuctionUI.lua:1961: AuctionFrameItem_OnEnter()
...uc-Advanced\Modules\Auc-Util-CompactUI\CompactUI.lua:513:
...uc-Advanced\Modules\Auc-Util-CompactUI\CompactUI.lua:507
Locals:

AddOns:
Swatter, v5.21e.5566 (SanctimoniousSwamprat)
WowheadLooter, v60011
Altoholic, vr164
AraBrokerGuildFriends, vr72
Atlas, v1.32.00
AtlasCataclysm, v1.32.00
AtlasDungeonLocs, v1.32.00
AtlasMistsofPandaria, v1.32.00
AtlasOutdoorRaids, v1.32.00
AtlasTransportation, v1.32.00
AtlasWorldEvents, v3.13
AtlasWrathoftheLichKing, v1.32.00
AtlasLoot, vv8.00.40
AucAdvanced, v5.21e.5566 (SanctimoniousSwamprat)
AucFilterOutlier, v5.21e.5566.5459(5.21e/embedded)
AucMatchUndercut, v5.21e.5566.5507(5.21e/embedded)
AucStatSales, v5.21e.5566.5476(5.21e/embedded)
AucStatWOWEcon, v5.21e.5566.5323(5.21e/embedded)
AucUtilAHWindowControl, v5.21e.5566.5347(5.21e/embedded)
AucUtilAppraiser, v5.21e.5566.5545(5.21e/embedded)
AucUtilAskPrice, v5.21e.5566.5447(5.21e/embedded)
AucUtilAutoMagic, v5.21e.5566.5537(5.21e/embedded)
AucUtilCompactUI, v5.21e.5566.5550(5.21e/embedded)
AucUtilEasyBuyout, v5.21e.5566.5507(5.21e/embedded)
AucUtilItemSuggest, v5.21e.5566.5417(5.21e/embedded)
AucUtilPriceLevel, v5.21e.5566.5535(5.21e/embedded)
AucUtilScanButton, v5.21e.5566.5403(5.21e/embedded)
AucUtilScanFinish, v5.21e.5566.5515(5.21e/embedded)
AucUtilScanProgress, v5.21e.5566.4979(5.21e/embedded)
AucUtilScanStart, v5.21e.5566.5347(5.21e/embedded)
AucUtilSearchUI, v5.21e.5566.5556(5.21e/embedded)
AucUtilSimpleAuction, v5.21e.5566.5531(5.21e/embedded)
AucUtilVendMarkup, v5.21e.5566.4828(5.21e/embedded)
Auctionator, v3.2.4
Auditor2, v5.0.1
Babylonian, v5.1.DEV.332(/embedded)
Bagnon, v6.2.4
BagnonConfig, v6.2.4
BattlePetBreedID, vv1.4.5
Bazooka, vv2.6.1
BazookaOptions, vv2.6.1
BetterBattlePetTooltip, v6.2.0.25
BrokerAuditor, v5.0.1
BrokerCurrency, v6.2.0.5
BrokerLocation, v1.14
cancelpetfight, vr46-release
Configator, v5.1.DEV.382(/embedded)
DataStore, vr55
DataStoreAchievements, vr40
DataStoreAgenda, vr22
DataStoreAuctions, v6.0.001
DataStoreCharacters, vr35
DataStoreContainers, vr51
DataStoreCrafts, vr68
DataStoreCurrencies, vr30
DataStoreGarrisons, vr14
DataStoreInventory, vr43
DataStoreMails, vr43
DataStorePets, vr38
DataStoreQuests, vr35
DataStoreReputations, vr36
DataStoreSpells, vr26
DataStoreStats, vr25
DataStoreTalents, vr51
DebugLib, v5.1.DEV.337(/embedded)
EasyLunkerTurnIn, v1.12
ElvUI, v8.23
ElvUIEnhanced, v3.1.0-beta5
ElvUIMicrobar, v1.77
iLvLr, v2.3.102
LibExtraTip, v5.12.DEV.390(/embedded)
LibPeriodicTable31, vv3.3.0.493
LibSharedMedia30, v3.0-93
MacroToolkit, vv6.2.0.0
PetJournalEnhanced, v2.9.16
PetShoppingList, v1.0
Postal, v3.5.4
SavedInstances, v6.2.2
Stubby, v5.21e.5566 (SanctimoniousSwamprat)
TipHelper, v5.12.DEV.389(/embedded)
TradeSkillMaster, vv2.10.26
TradeSkillMasterAccounting, vv2.4.5
TradeSkillMasterAdditions, vv2.1.6
TradeSkillMasterAppHelper, vv2.0.4
TradeSkillMasterAuctionDB, vv2.7.1
TradeSkillMasterAuctioning, vv2.4.6
TradeSkillMasterCrafting, vv2.6.19
TradeSkillMasterItemTracker, vv2.1.4
TradeSkillMasterMailing, vv2.2.13
TradeSkillMasterShopping, vv2.4.6
TradeSkillMasterWoWuction, vv2.5.3
zzInfoclock, v
BlizRuntimeLib_enUS v6.2.0.60200
(ck=c5f)

Duplicate of #5