TypeError: Cannot read property 'toString' of null

[fcobia]

When I have a field that is either "number" or "string" and I use just the plain decorator "@Attribute()" I get the error "TypeError: Cannot read property 'toString' of null" if the value is null. Evidently there needs to be a check for null somewhere before calling "toString."

It would be nice if it would not throw exceptions for null values.

I have had to work around this by doing the following:

	@attribute(
		{
			type: 'Custom',
			marshall: (value) => {
				
				return value ? {N: value.toString()} : null;
			},
			unmarshall: (attributeValue) => Number(attributeValue.N),
		})

[jeskew]

If the error is reproducible, could you grab a stack trace?

[fcobia]

I did a little more digging and I also created a test that reproduces the error. You can find it at https://github.com/fcobia/DataMapperBug.

It turns out that if I do not set a value to 'null' and it just defaults to null then it works as expected. If I explicitly set the value to null then you get the error.

[jeskew]

Properties for which no value has been set are undefined in JavaScript, which the mapper checks for and interprets as the absence of a property. null is distinct from undefined and can be stored in DynamoDB as a sigil value.

In TypeScript, the optional marker (?) indicates that a property may be undefined but doesn't imply that the property may be assigned a value of null.

[fcobia]

I get what you are saying (and this is one of the many things I hate about Javascript), but that still leaves me with 2 problems:

1. The mapper tries to call "toString()" on null which causes an exception and brings the program to a halt.

2. What if I want null values to be ignored?

[jeskew]

The marshaller could have a configuration option to treat null as undefined. As a workaround, you could declare the property in a way that captures all three types it could be:

class MyClass {
    @attribute()
    property?: number|null;
}

@jeskew Should the above allow number or null? I have set up this for both string and number type.
null throws the same error on both:

"TypeError: Cannot read property 'toString' of null", at marshallNumber

I'm struggling to manage a flow that allows null values so I can update the DB with a { onMissing: "skip" } but also allow the removal of values i intend to be nulled.

[fcobia]

@jeskew Can't the underlying code check for null and undefined before calling "toString()"? I understand that there is a difference between null and undefined, but I do not consider this a feature request since javascript does not allow calling toString() on null.

Shouldn't this be considered a bug if it causes the library to throw an error when passing an allowed value?

[harryhan24]

At this moment, DynamoDB have started support to empty value. , but still i got 'cannot read property 'toString' of null'. any update about it?