Not quite right. null !== NULL
NULL is an Object of type State and it is a special State Items can have to indicated the Item is uninitialized. As an Object, NULL does have a .equals method so == should be used.
null is a primitive speical work in the programming langauge to indicate no value. As a primitive, null does not have a .equals method so one should use the identity operator === instead of the equivalency operator ==.
So === and !== should only be used with null and never used with NULL.
Its confusing and I rue the day they changed from using UNDEF to using NULL.
From what version of OH did you upgrade from?
Do not import anything from org.eclipse.smarthome. They are already imported for you.
When you Rule runs Rolladen_OG_Bad’s state is NULL. NULL is not of type DecimalType so you cannot cast it to DecimalType. As for why that is the case I cannot say but as long as that Item’s state remains NULL, that line as written will always generate an error. To avoid the error you need to do something like:
var int actual = -1
if(Rolladen_OG_Bad.state == NULL) {
// what to do in an error
}
else {
actual = (Rolladen_OG_Bad.state as DecimalType).intValue
}