ContentNote not inserting

Question

I am trying to insert a new ContentNote and link it to an opportunity with ContentDocumentLink. However, after inserting the content note, the ID returns as NULL, so referencing it in the ContentDocumentLink causes an error. What may be the issue here?

// Step 1, create new Note          
ContentNote cn = new ContentNote(
  Title = 'Title',
  Content = Blob.valueOf('Dummy')
);          
insert cn; //After this insert, cn.Id is NULL

// Step 2, create the ContentDocumentLink
ContentDocumentLink cdl = new ContentDocumentLink();           
cdl.ContentDocumentId = cn.Id; //Referencing cn.Id causes error
cdl.LinkedEntityId = opp.Id;          
cdl.Visibility ='AllUsers';
cdl.ShareType ='V';

insert cdl;

Inserting a classic Note has no issues at all.

note n = new note();
n.parentId= opp.Id;
n.body=inputArray;
n.title='Array';
n.isPrivate=false;
insert n;

Answer 1

It appears to me from looking at the Object Reference for ContentNote the issue is with your method for inserting the note.

They give two examples and both show discrepancies with how you're creating the content's body which has to do with escaping the HTML from the enhanced note. Below are the two relevant examples.

Example 1:

ContentNote cn = new ContentNote();
cn.Title = 'test1';
String body = 'Hello World. Before insert/update, escape special characters such as ", ', &, and other standard escape characters.';
cn.Content = Blob.valueOf(body.escapeHTML4());
insert(cn);

Example 2:

ContentNote cn = new ContentNote();
cn.Title = 'test2';
String body = '<b>Hello World. Because this text is already formatted as HTML, it does not need to be escaped. 
Special characters such as &quot;, etc. must already use their HTML equivalents.</b>';
cn.Content = body;
insert(cn);

I recommend you give one of the above methods a try and see if it doesn't resolve your issue.