Odin confusion with nil

nil.odin

package main

import "core:fmt"

Test :: struct {
	test: int
}

EnumTest :: enum {
	Int,
	String,
}

UnionTest :: union {
	EnumTest,
	Test,
}

UnionTestNotNil :: union #no_nil {
	Test,
	EnumTest,
}

main :: proc() {
	a : Test
	// Won't compile, nil can't be a Test
	// if a == nil {
	//	 fmt.println("Test, it was nil")
	// } else {
	//	 fmt.println("Test, it was NOT nil")
	// }
	fmt.println("%v", a)
	//> %v Test{test = 0}

	b : EnumTest
	if b == nil {
		fmt.println("EnumTest, it was nil")
	} else {
		fmt.println("EnumTest, it was NOT nil")
	}
	//> EnumTest, it was nil
	fmt.println("%v", b)
	//> %v Int

	c : UnionTest
	if c == nil {
		fmt.println("UnionTest, it was nil")
	} else {
		fmt.println("UnionTest, it was NOT nil")
	}
	//> UnionTest, it was nil
	fmt.println("%v", c)
	//> %v nil

	d : UnionTestNotNil
	// Won't compile, nil can't be a UnionTestNotNil
	// if d == nil {
	// 	fmt.println("UnionTestNotNil, it was nil")
	// } else {
	// 	fmt.println("UnionTestNotNil, it was NOT nil")
	// }
	fmt.println("%v", d)
	//> %v Test{test = 0}
}