Calling ItemStack.getData() or ItemStack.setData(...) causes legacy material support initialization{{}}:

Initializing Legacy Material Support. Unless you have legacy plugins and/or data this is a bug!

The server freezes for a second while it does some legacy material magic before returning a legacy material (e.g. LEGACY_DIRT, instead of{{ DIRT}}).

The documentation does not mention this behavior.

As I feel we all would prefer to work with new, better DIRT over old, horrible LEGACY_DIRT, I think the method should be annotated as deprecated and/or the documentation should be updated to make users aware of this (misleading) behavior.

One of the methods in question looks like so:

/**
{{ * Gets the MaterialData for this stack of items}}
{{ *}}
{{ * @return MaterialData for this item}}
{{ */}}
@Nullable
public MaterialData getData() {
    Material mat = Bukkit.getUnsafe().toLegacy(getType());
    if (data == null && mat != null && mat.getData() != null) {
        data = mat.getNewData((byte) this.getDurability());
{{    }}}

    return data;
}