What does “I have no son after whom I took my kunya” establish?

The Kūfan Maqāmah: The Lost-Son Secret and Abū Zayd’s Final Ruse

• Zayd is a place name
• Al-Ḥārith is Abū Zayd’s son
• A kunya does not necessarily establish a literal son
• Abū Zayd has no name