use keywords as arrays in list

nf_core/components/list.py

@@ -18,7 +18,7 @@ def __init__(self, component_type, pipeline_dir, remote=True, remote_url=None, b
         super().__init__(component_type, pipeline_dir, remote_url, branch, no_pull)
         self.remote = remote
 
-    def list_components(self, keywords=None, print_json=False):
+    def list_components(self, keywords=[], print_json=False):
         """
         Get available modules/subworkflows names from GitHub tree for repo
         and print as list to stdout
@@ -31,9 +31,6 @@ def list_components(self, keywords=None, print_json=False):
         table.add_column(f"{self.component_type[:-1].capitalize()} Name")
         components = []
 
-        if keywords is None:
-            keywords = []
-
         def pattern_msg(keywords):
             if len(keywords) == 0:
                 return ""