Nullable and optional properties

This is a:

• Bug Report
• Feature Request
• Question
• Other

Which concerns:

• flow-runtime
• babel-plugin-flow-runtime
• flow-runtime-validators
• flow-runtime-mobx
• flow-config-parser
• The documentation website

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What is the current behaviour?

Making a property of a type nullable behaves the same as if it was optional.

const A = t.type("A", t.object(t.property("a", t.nullable(t.boolean()))));
const B = t.type("B", t.object(t.property("a", t.boolean(), true)));

A.assert({}); // passes
B.assert({}); // passes

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What is the expected behaviour?

I was expecting that a nullable property has to be set, but accepts null values, and optional properties may be omitted.

A.assert({a: null}); // passes
A.assert({a: undefined}; // passes
A.assert({}); // fails (property "a" does not exist)

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Which package versions are you using?

I used the live demo: https://codemix.github.io/flow-runtime

[samhagan]

@fabiandev thanks for the quick reply. I hadn’t noticed that…this is happening to us on api boundaries, so the strictness just highlighted bad type definitions.

[samhagan]

This change seems inconsistent with Flow, which allows { field: ?number } to be null, undefined/void, or a number, which means that it can also be omitted. This is preventing us from upgrading from 0.12.0 without some material type changes. Could we make this configurable via options? Happy to look at doing a PR.