Fix default values of multiple options with optional values

CHANGES.rst

@@ -24,6 +24,8 @@ Unreleased
     :issue:`2072`
 -   Default values are not cast to the parameter type twice during
     processing. :issue:`2085`
+-   Options with ``multiple`` and ``flag_value`` use the flag value
+    instead of leaving an internal placeholder. :issue:`2001`
 
 
 Version 8.0.1

src/click/core.py

@@ -2853,6 +2853,14 @@ def consume_value(
                 value = self.flag_value
                 source = ParameterSource.COMMANDLINE
 
+        elif (
+            self.multiple
+            and value is not None
+            and any(v is _flag_needs_value for v in value)
+        ):
+            value = [self.flag_value if v is _flag_needs_value else v for v in value]
+            source = ParameterSource.COMMANDLINE
+
         # The value wasn't set, or used the param's default, prompt if
         # prompting is enabled.
         elif (

tests/test_options.py

@@ -792,6 +792,29 @@ def cli(opt, a, b):
     assert result.return_value == expect
 
 
+def test_multiple_option_with_optional_value(runner):
+    cli = click.Command(
+        "cli",
+        params=[
+            click.Option(["-f"], is_flag=False, flag_value="flag", multiple=True),
+            click.Option(["-a"]),
+            click.Argument(["b"], nargs=-1),
+        ],
+        callback=lambda **kwargs: kwargs,
+    )
+    result = runner.invoke(
+        cli,
+        ["-f", "-f", "other", "-f", "-a", "1", "a", "b"],
+        standalone_mode=False,
+        catch_exceptions=False,
+    )
+    assert result.return_value == {
+        "f": ("flag", "other", "flag"),
+        "a": "1",
+        "b": ("a", "b"),
+    }
+
+
 def test_type_from_flag_value():
     param = click.Option(["-a", "x"], default=True, flag_value=4)
     assert param.type is click.INT