Extra GL line entry after posting Sales Invoice

Hi,

I have processed transaction in the following scenario, and I have a general question with regards to the resulting GL Entries.

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1. Create Sales Order with Total Amount of $80,000.00
2. Post Prepayment of 50%. ($40,000.00)
3. Post Cash Receipt against the Prepayment.
4. Post another Prepayment of 50%. ($40,000.00)
5. Post Cash Receipt against the 2nd Prepayment.
6. Post Sales Invoice.
7. Check GL Entries
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When I check the GL entries, I see the following 3 entries.
Sales of Retail: -$80,000.00
Prepayments: $80,000.00
A/R: $0.00

Why does the last A/R entry shows up on the GL Entry, even though its $0.00?
It seems like an unnecessary entry if it has no values.

Thank you.