diff --git a/src/event/FullyBufferedSocket.cxx b/src/event/FullyBufferedSocket.cxx
index e7869cd66..375132e34 100644
--- a/src/event/FullyBufferedSocket.cxx
+++ b/src/event/FullyBufferedSocket.cxx
@@ -60,7 +60,7 @@ FullyBufferedSocket::Flush()
 	assert(IsDefined());
 
 	const auto data = output.Read();
-	if (data.IsNull()) {
+	if (data.IsEmpty()) {
 		IdleMonitor::Cancel();
 		CancelWrite();
 		return true;
diff --git a/src/util/PeakBuffer.cxx b/src/util/PeakBuffer.cxx
index c66218043..5e86503e8 100644
--- a/src/util/PeakBuffer.cxx
+++ b/src/util/PeakBuffer.cxx
@@ -43,13 +43,13 @@ PeakBuffer::Read() const
 {
 	if (normal_buffer != nullptr) {
 		const auto p = normal_buffer->Read();
-		if (!p.IsNull())
+		if (!p.IsEmpty())
 			return p.ToVoid();
 	}
 
 	if (peak_buffer != nullptr) {
 		const auto p = peak_buffer->Read();
-		if (!p.IsNull())
+		if (!p.IsEmpty())
 			return p.ToVoid();
 	}
 
@@ -85,7 +85,7 @@ AppendTo(DynamicFifoBuffer<uint8_t> &buffer, const void *data, size_t length)
 
 	do {
 		const auto p = buffer.Write();
-		if (p.IsNull())
+		if (p.IsEmpty())
 			break;
 
 		const size_t nbytes = std::min(length, p.size);