Transmog button does not work with ElvUI

[Pairaka]

Have learnable items in my bags, use the Transmog button and nothing happens (with ElvUI bags enabled). Got this error:

2x HelpMePlay/Systems/Transmog.lua:42: attempt to call global 'GetContainerNumSlots' (a nil value)
[string "@HelpMePlay/Systems/Transmog.lua"]:42: in function <HelpMePlay/Systems/Transmog.lua:40>

Locals:
(for index) = 0
(for limit) = 4
(for step) = 1
i = 0
(*temporary) = 1
(*temporary) = nil
(*temporary) = 0
(*temporary) = "attempt to call global 'GetContainerNumSlots' (a nil value)"
RequipOriginalItems = defined @HelpMePlay/Systems/Transmog.lua:15
equippedItems =

{
1 = {
}
2 = {
}
3 = {
}
4 = {
}
5 = {
}
6 = {
}
7 = {
}
8 = {
}
9 = {
}
10 = {
}
11 = {
}
12 = {
}
}

[Pairaka]

Related to this issue: Disabling ElvUI bags causes the Transmog button to not show at all, and gives this error:

1x HelpMePlay/Systems/Transmog.lua:154: attempt to index global 'ElvUI_ContainerFrame' (a nil value)
[string "@HelpMePlay/Systems/Transmog.lua"]:154: in function <HelpMePlay/Systems/Transmog.lua:152>

Locals:
(*temporary) = nil
(*temporary) = nil
(*temporary) = "TOPRIGHT"
(*temporary) = nil
(*temporary) = "TOPLEFT"
(*temporary) = -5
(*temporary) = -1
(*temporary) = "attempt to index global 'ElvUI_ContainerFrame' (a nil value)"
HMPTransmogButton = HMPTransmogButton {
SetTextToFit = defined @SharedXML/SecureUIPanelTemplates.lua:440
Right = Texture {
}
Left = Texture {
}
fitTextWidthPadding = 40
FitToText = defined @SharedXML/SecureUIPanelTemplates.lua:445
Text = HMPTransmogButtonText {
}
0 =
Middle = Texture {
}
fitTextCanWidthDecrease = true
}

[Saaappi]

The second error is technically a different problem. I've opened a separate issue for it.

[Saaappi]

The first error is fixed in 20f2ebf.