[Baertram]

Maybe I got you wrong but you tried to use namespace as an "optional argument". So why don't you just put nil in the correct place as you call the function?

ZO_SavedVars:New("TestSV",1, nil, {},"TestProfile")

Edit:
Oh sorry just saw the lines 142ff in the sourcecode and now I understood what you are up to

--namespace is an optional argument
    if defaults == nil and type(namespace) == "table" then
        profile = defaults
        defaults = namespace        
        namespace = nil
    end
    profile = profile or "Default"
    if type(profile) ~= "string" then
        error("Profile must be a string or nil")
    end

Here are the prameters of the function GetNewSavedVars from the live server:

local function GetNewSavedVars(savedVariableTable, version, namespace, defaults, profile, displayName, characterName, characterId, characterKeyType)

Parameters of ZO_SavedVars:New()

function ZO_SavedVars:New(savedVariableTable, version, namespace, defaults, profile, displayName, characterName, characterId, characterKeyType)

If you use ZO_SavedVars:New from your example:

ZO_SavedVars:New("TestSV",1,{},"TestProfile")

savedVariableTable: "TestSV"
version: 1
namespace: {}
defaults: "TestProfile"
profile: nil