Fix echoing empty binary messages

src/click/utils.py

@@ -294,11 +294,11 @@ def echo(
         out = message
 
     if nl:
-        out = out or ""
-        if isinstance(out, str):
-            out += "\n"
+        if isinstance(out, (bytes, bytearray)):
+            out = out + b"\n"
         else:
-            out += b"\n"
+            out = out or ""
+            out += "\n"
 
     if not out:
         file.flush()

tests/test_utils.py

@@ -8,6 +8,7 @@
 from decimal import Decimal
 from fractions import Fraction
 from functools import partial
+from io import BytesIO
 from io import StringIO
 from unittest.mock import patch
 
@@ -92,6 +93,21 @@ def cli():
         assert outstreams[0].getvalue() == b"\x1b[31mx\x1b[39m"
 
 
+@pytest.mark.parametrize("message_type", [bytes, bytearray])
+def test_echo_empty_bytes(message_type, runner):
+    with runner.isolation() as outstreams:
+        click.echo(message_type())
+        assert outstreams[0].getvalue().replace(b"\r\n", b"\n") == b"\n"
+
+    f = BytesIO()
+    click.echo(message_type(), file=f)
+    assert f.getvalue() == b"\n"
+
+    f = BytesIO()
+    click.echo(message_type(), nl=False, file=f)
+    assert f.getvalue() == b""
+
+
 def test_echo_custom_file():
     f = StringIO()
     click.echo("hello", file=f)