Is there a defined minimal interface for a type to work with SparseArrays?

Internals & Design
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3

My Julia version is 1.6.3. But even testing my code with 1.7 (or even master) it does not work. It seems that it is accepted the interface of zero and iszero. But in some other places != zero and == zero is used instead of !iszero and iszero.

Which in this case makes SparseArrays to not work with Num given that (if a is a symbolic variable) a != zero(a) returns an Expression instead of a Bool.

MWE (Julia 1.6.3, latest Symbolics)

using Symbolics
using SparseArrays

@variables a

v = sparsevec([1], [v])

v+v # here throws an error