How do I keep a running count in Google Sheets with skipped lines?

I have a Google Sheet that looks like this:

A           |
Group 1     |
Lorem       |
Ipsum       |
Dolor       |
null        |
Group 2     |
Sit         |
Amet        | 
Consectetur |

I would like to create a new column (preferably in column A) that keeps a running count of entries, skipping the blank rows ("null"), and skipping the Group headers.

A     | B
null  | Group 1 
1     | Lorem 
2     | Ipsum 
3     | Dolor 
null  | null   
null  | Group 2 
4     | Sit 
5     | Amet  
6     | Consectetur 

If an entry is added or deleted, then the desired output would automatically update the numbering.