fix: handle values null better (#39)

README.md

@@ -185,6 +185,18 @@ cy
 
 See spec [alias.cy.js](./cypress/e2e/alias.cy.js)
 
+## Null values
+
+Typically `null` values are treated same as `undefined` and follow the "else" path. You can specifically check for `null` and `not.null` using these assertions:
+
+```js
+cy.wrap(null).if('null') // takes IF path
+cy.wrap(null).if('not.null') // takes ELSE path
+cy.wrap(42).if('not.null') // takes IF path
+```
+
+See spec [null.cy.js](./cypress/e2e/null.cy.js)
+
 ## More examples
 
 Check out the spec files in [cypress/e2e](./cypress/e2e/) folder. If you still have a question, [open a GitHub issue](https://github.com/bahmutov/cypress-if/issues).

cypress/e2e/null.cy.js

@@ -0,0 +1,40 @@
+/// <reference types="cypress" />
+// @ts-check
+
+import '../../src'
+
+// https://github.com/bahmutov/cypress-if/issues/38
+describe('null value', () => {
+  it('handles null assertion', () => {
+    cy.wrap(null)
+      .if('null')
+      .log('null value')
+      .then(cy.spy().as('if'))
+      .else()
+      .then(cy.spy().as('else'))
+    cy.get('@if').should('have.been.called')
+    cy.get('@else').should('not.have.been.called')
+  })
+
+  it('handles not.null assertion', () => {
+    cy.wrap(null)
+      .if('not.null')
+      .log('null value')
+      .then(cy.spy().as('if'))
+      .else()
+      .then(cy.spy().as('else'))
+    cy.get('@else').should('have.been.called')
+    cy.get('@if').should('not.have.been.called')
+  })
+
+  it('handles 42 with not.null assertion', () => {
+    cy.wrap(42)
+      .if('not.null')
+      .log('null value')
+      .then(cy.spy().as('if'))
+      .else()
+      .then(cy.spy().as('else'))
+    cy.get('@if').should('have.been.called')
+    cy.get('@else').should('not.have.been.called')
+  })
+})

src/index.js

@@ -68,7 +68,15 @@ Cypress.Commands.add(
       // set the subject and the assertions to take the IF branch
       hasSubject = Cypress._.get(cmd, 'attributes.prev.attributes.error')
     } else {
-      if (hasSubject && assertion) {
+      if (subject === null) {
+        if (assertion === 'null') {
+          hasSubject = true
+          assertionsPassed = true
+        } else if (assertion === 'not.null') {
+          hasSubject = true
+          assertionsPassed = false
+        }
+      } else if (hasSubject && assertion) {
         try {
           if (Cypress._.isFunction(assertion)) {
             const result = assertion(subject)