cannot set properties of null (setting 'innerhtml')

[pashasapcha]

Hi, I am learning js . I am facing error

VM20 custom.js:23 Uncaught TypeError: Cannot set properties of null (setting 'innerHTML')

at readData (VM20 custom.js:23:41)

at onload (Welcome.html:14:29)

The following are the screenshots

index.html

custom.js

welcome.html

but I am not getting the username that is given in the input when I execute t.