Fix issue #516

src/sakia/core/wallet.py

@@ -190,6 +190,7 @@ class Wallet(QObject):
 
         amount, amount_base = reduce_base(amount, 0)
         cache = self.caches[community.currency]
+        if cache.available_sources:
             current_base = max([src['base'] for src in cache.available_sources])
             value = 0
             sources = []