command options: allow for default values

src/poetry/console/commands/add.py

@@ -107,7 +107,7 @@ You can specify a package in the following forms:
             )
             group = "dev"
         else:
-            group = self.option("group")
+            group = self.option("group", self.default_group or MAIN_GROUP)
 
         if self.option("extras") and len(packages) > 1:
             raise ValueError(

src/poetry/console/commands/command.py

 from __future__ import annotations
 
 from typing import TYPE_CHECKING
+from typing import Any
 
 from cleo.commands.command import Command as BaseCommand
+from cleo.exceptions import ValueException
 
 
 if TYPE_CHECKING:
@@ -30,3 +32,9 @@ class Command(BaseCommand):
 
     def reset_poetry(self) -> None:
         self.get_application().reset_poetry()
+
+    def option(self, name: str, default: Any = None) -> Any:
+        try:
+            return super().option(name)
+        except ValueException:
+            return default

src/poetry/console/commands/group_command.py

@@ -61,6 +61,16 @@ class GroupCommand(EnvCommand):
         }
 
     @property
+    def default_group(self) -> str | None:
+        """
+        The default group to use when no group is specified. This is useful
+        for command that have the `--group` option, eg: add, remove.
+
+        Can be overridden to adapt behavior.
+        """
+        return None
+
+    @property
     def default_groups(self) -> set[str]:
         """
         The groups that are considered by the command by default.

src/poetry/console/commands/install.py

@@ -80,7 +80,7 @@ dependencies and not including the current project, run the command with the
         )
 
         extras = []
-        for extra in self.option("extras"):
+        for extra in self.option("extras", []):
             if " " in extra:
                 extras += [e.strip() for e in extra.split(" ")]
             else:

src/poetry/console/commands/remove.py

@@ -48,7 +48,7 @@ list of installed packages
             )
             group = "dev"
         else:
-            group = self.option("group")
+            group = self.option("group", self.default_group)
 
         content = self.poetry.file.read()
         poetry_content = content["tool"]["poetry"]
@@ -106,7 +106,7 @@ list of installed packages
             self.poetry.config.get("experimental.new-installer", False)
         )
 
-        self._installer.dry_run(self.option("dry-run"))
+        self._installer.dry_run(self.option("dry-run", False))
         self._installer.verbose(self._io.is_verbose())
         self._installer.update(True)
         self._installer.whitelist(removed_set)