Solution Link - Link requested?

How does one solve the code issues in this starting from the Quality Assurance in order to go on to the next one… it basically says this:

Within tests/1_unit-tests.js under the test labelled #1 in the Basic Assertions suite, change each assert to either assert.isNull or assert.isNotNull to make the test pass (should evaluate to true ). Do not alter the arguments passed to the asserts.

Please help ?

what parts do you find confusing here?