Unit test code fails by stating UnhandledPromiseRejectionWarning: TypeError: Cannot convert undefined or null to object in node js with mocha chai

Question

index .js

module.exports = {
  
  addDetails: function() {
    let data =[]
    data.push("one");
    return data
  },

  deleteDetails: function() {
    let data =["one" , "two"]
    data.splice(0 , 1)
    return data
  },

  editDetails: function() {
    let data =["one"]
    data.splice(0 , 1 , "three")
    return data
  },

  updateDetails: function() {
    let data = ["one" , "three"]
    data.splice(1 , 0 , "two")
    return data
  },

  detailsPop: function() {
    let numb = ["one" , "two"]
    numb.pop()
    return numb
  },

  concatData: function() {
    let data1 = ["one"]
    let data2 = ["two"]
    let result = data1.concat(data2)
    return result
  }
 }

indextest.js

var assert = require("assert");
var crud = require('../src/index');

describe('Crud application', ()=>{
    //write your code here
    it('should add "one" to the array', async() => {
      const result = await crud.addDetails();
      assert.deepEqual(result, ['one']);
    });

    it('should delete the first element from the array', async() => {
      const result = await crud.deleteDetails();
      assert.deepEqual(result, ['two']);
      console.log(2)
    });
  
    it('should replace "one" with "three" in the array', async() => {
      const result = await crud.editDetails();
      assert.deepEqual(result, ['three']);
    });
  
    it('should update the array with "two" between "one" and "three"', async() => {
      const result = await crud.updateDetails();
      assert.deepEqual(result, ['one', 'two', 'three']);
    });
  
    it('should remove the last element from the array', async() => {
      const result = await crud.detailsPop();
      assert.deepEqual(result, ['one']);
    });
  
    it('should concatenate two arrays', async() => {
      const result = await crud.concatData();
      assert.deepEqual(result, ['one', 'two']);
    });
    it("Don't remove this dummy test case as its required for validation", async() => {
        const dummy = [{}];
        dummy.should.have.length(1);
    });
});

mocha --timeout 10000 --reporter mocha-junit-reporter --collectCoverageFrom=src/index.js --exit

The test code always fails by saying

mocha --timeout 10000 --reporter mocha-junit-reporter --collectCoverageFrom=src/index.js --exit

Error :

(node:2059) UnhandledPromiseRejectionWarning: TypeError: Cannot convert undefined or null to object