Null Value Operations

Generally, if a null value is one of the arguments of a function/operator, the result would be null.

x = 1.0 + 5.6 * 3 + NULL + 3
isNull(x)
// output: 1

typestr x;
// output: DOUBLE

However, there are special cases as follows:

With comparison operators >, >=, <, <=, and between, null values represent the minimum value when the configuration parameter nullAsMinValueForComparison is set to true (default). When it is set to false, the comparison result is null.
```
// nullAsMinValueForComparison = true
1 < NULL // output: false
1 > NULL // output: true

// nullAsMinValueForComparison = false
1 < NULL // output: 00b
1 > NULL // output: 00b
```
With comparison operators !=, <>, and ==, null values represent the minimum value and two null values are considered equal.
```
NULL == NULL // output: true
NULL != NULL // output: false
```
In the or function, if only one operand is null, the result is equal to the other non-null operand when the configuration parameter logicOrIgnoreNull is set to true (default). When it is set to false, the result is null is one operand is null.
```
// logicOrIgnoreNull = true
NULL or true // output: true
NULL or false // output: false
NULL or NULL // output: 00b

// logicOrIgnoreNull = false

NULL or true // output: 00b
NULL or false // output: 00b
NULL or NULL // output: 00b
```
In aggregate functions such as sum/avg/med, null values are ignored.
```
x = 1 2 NULL NULL 3;
sum(x)
// output: 6

avg(x)
// output: 2
```
When sorting elements in a vector, null values represent the minimum value.
In functions ols/olsEx/corrMatrix/olsEx, null values in parameters are replaced with 0.