null.md

Null values

Null values are special property values that represent the absence of a value. They are used to indicate that a property is intentionally empty or missing.

null values cannot be used as a ID of components because it is reserved word.

Setting a property to null works differently for different statements.

null in #insert and #update

When we set a property to null in the #insert or #forceInsert statements, it means that the property is intentionally empty,missing, or has the default value. It is the same as we do not declare the property at all.

k1 @Const {units: null} = 1; // implicit #insert

works the same as

k1 @Const = 1;

When we set a property to null in the #update statement, it means that the property is intentionally removed.

k1 @Const {units: mM};
k1 {units: null} = 1; // implicit #update

which is equivalent to

k1 @Const = 1;

wrong usage of null

Null properties are allowed only in properties but not in sub-properties like in examples below.

x1 @Record {
    aux: {a: 1, b: null} // throw syntax error
}; 

x1 @Record {
    aux: null // correct
}; 

x1 @Record {
    tags: [a, b, null] // throw syntax error
}; 

x1 @Record {
    tags: null // correct
}; 

Null properties values must be used only for components, but not for #defineFunction or #defineUnit.

#defineFunction f1 {
    arguments: [x,y,z],
    math: null          // throw syntax error
};

#defineUnit u1 {
    units: null          // throw syntax error
};

Null value cannot be used as a ID of components.

null @Const = 1; // throw syntax error