[fix] When normalize() receives null input, don't say it is an object

[ntucker]

Problem

In Javascript typeof null === 'object'.

Solution

Since the check in normalize includes one for !input, it should say 'found null' when null is passed rather than a confusing message that it found object when it needed object.

TODO

• Add & update tests
• Ensure CI is passing (lint, tests, flow)
• Update relevant documentation

[coveralls]

Coverage remained the same at 100.0% when pulling dff77ac on ntucker:normalize-null-input into b5f570a on paularmstrong:master.

[paularmstrong]

nit: toThrow('Unexpected input given to normalize')

[ntucker]

Just making sure it has null in the error string. Not trying to worry about the rest of the wording since there isn't an conditional in there.

[paularmstrong]

Maybe derive the type from the schema? array if Array.isArray(schema) || schema instanceof schema.Array

[ntucker]

I don't believe an array would trigger this. typeof myarray === 'object' and all arrays are truthy.

[ntucker]

null, undefined, numbers, strings, symbols, functions (and thus static classes as well) are the only types that would trigger this. maybe some other primitive type I'm not aware of.

[paularmstrong]

I mean derive the type for the expectation to say: Expected type to be "${Array.isArray(schema) || schema instanceof schema.Array ? 'array' : 'object'}"

[ntucker]

ahh, gotcha. yes this is a good additional improvement

[ntucker]

but then shouldn't it fail if you get an array when expecting a plain object? currently this check will pass

[ntucker]

Should I add a respective test for array vs plain object in the if statement?

[ntucker]

Seems like array and objects are interchangable due to tests like:

    test('normalizes Objects using their values', () => {
      const userSchema = new schema.Entity('user');
      const users = new schema.Array(userSchema);
      expect(normalize({ foo: { id: 1 }, bar: { id: 2 } }, users)).toMatchSnapshot();
    });

[ntucker]

Realized it would be weird to output other falsy things like 0, so I explicitly only handle null case in special way now.