Could not execute mockbuild: Could not download sources

When writing a .spec file for Fedora, I ran into a problem. I can't seem to be able to do fedpkg mockbuild at all. No matter what source I use, HTTPS or local, I keep running into this error:

Failed to get repository name from Git url or pushurl
Failed to get ns from Git url or pushurl
Could not execute mockbuild: ('Could not download sources: %s', AttributeError("'NoneType' object has no attribute 'head'"))

What's going on? The relevant part of my .spec file:

Name:           purple-telegram-tdlib
# The main maintainer has not merged #154 for TDLib 1.8.0
Version:        0.8.1-BenWiederhake
Release:        1%{?dist}
Summary:        New libpurple plugin for Telegram

License:        GPLv2
URL:            https://github.com/ars3niy/tdlib-purple 
Source0:        tdlib-purple-BenWiederhake-master.zip

BuildRequires:  gcc-c++
BuildRequires:  git
BuildRequires:  make
BuildRequires:  cmake
BuildRequires:  tdlib-devel == 1.8.0
BuildRequires:  tdlib-static == 1.8.0
BuildRequires:	libpurple-devel
BuildRequires:	libwebp-devel
BuildRequires:	libpng-devel
BuildRequires:	gettext-devel