$value\;\text{IS NULL}$

'Alpha'

$\text{FALSE}$

$\text{TRUE}$

'Beta'

$\text{FALSE}$

'Gamma'

$\text{FALSE}$

$\text{TRUE}$

$value = \text{NULL}$

'Alpha'

$\text{UNKNOWN}$

$\text{UNKNOWN}$

'Beta'

$\text{UNKNOWN}$

'Gamma'

$\text{UNKNOWN}$

$\text{UNKNOWN}$