# Add the value of `v_expr` to `explain_str` and protect null values
	fun explain_expr(v_expr: AExpr)
	do
		var mtype = v_expr.mtype
		if mtype == null then
			explain_string "<unexpected error>"
			return
		end

		# Set the expression value aside
		var old_parent = v_expr.parent
		var expr = v_expr.make_var_read
		if old_parent != null then old_parent.validate

		# Protect nullable types
		if mtype isa MNullType then
			explain_string "null"
			return
		else if mtype isa MNullableType then
			var e = new AOrElseExpr
			e.n_expr = expr
			e.n_expr2 = explain_string("null", false)
			e.location = assert_node.location
			e.mtype = mmodule.object_type

			explain_str.n_exprs.add e
			return
		end

		explain_str.n_exprs.add expr
	end