diff --git a/src/compas_timber/ghpython/components/CT_Joint_Rule_Category/code.py b/src/compas_timber/ghpython/components/CT_Joint_Rule_Category/code.py
index 9c5a1b66f..60c813f7f 100644
--- a/src/compas_timber/ghpython/components/CT_Joint_Rule_Category/code.py
+++ b/src/compas_timber/ghpython/components/CT_Joint_Rule_Category/code.py
@@ -7,22 +7,27 @@
 from compas_timber.ghpython import manage_dynamic_params
 
 
-
 class CategoryJointRule(component):
     def RunScript(self, joint_options, *args):
-        names = [name + " category" for name in joint_options.beam_names]
+        if joint_options:
+            names = [name + " category" for name in joint_options.beam_names]
+        else:
+            names = None
+
+        manage_dynamic_params(names, ghenv)
 
-        manage_dynamic_params(names)
+        if not args or not names:  # check that dynamic params generated
+            return
 
-        if len(args) != len(names):  # check that dynamic params are correct
+        if len(args) != len(names):  # check that dynamic params generated correctly
             self.AddRuntimeMessage(Error, "Input parameter error.")
+            return
 
         create_rule = True
         for i in range(len(names)):
             if not args[i]:
                 self.AddRuntimeMessage(
-                    Warning,
-                    "Input parameter {} {} failed to collect data.".format(names[i], "categories"),
+                    Warning, "Input parameter {} {} failed to collect data.".format(names[i], "categories")
                 )
                 create_rule = False
         if create_rule:
diff --git a/src/compas_timber/ghpython/components/CT_Joint_Rule_Direct/code.py b/src/compas_timber/ghpython/components/CT_Joint_Rule_Direct/code.py
index 72f6a9a9d..9b908d035 100644
--- a/src/compas_timber/ghpython/components/CT_Joint_Rule_Direct/code.py
+++ b/src/compas_timber/ghpython/components/CT_Joint_Rule_Direct/code.py
@@ -11,27 +11,35 @@
 
 class DirectJointRule(component):
     def RunScript(self, joint_options, *args):
+        names = None
+        if joint_options:
+            names = [name + " category" for name in joint_options.beam_names]
 
-        manage_dynamic_params(joint_options.beam_names)
+        manage_dynamic_params(names, ghenv)
 
-        if len(args) != len(joint_options.beam_names):  # check that dynamic params are correct
+        if not args or not names:  # check that dynamic params generated
+            return
+
+        if len(args) != len(names):  # check that dynamic params generated correctly
             self.AddRuntimeMessage(Error, "Input parameter error.")
+            return
 
         beams = []
         create_rule = True
         for i in range(len(joint_options.beam_names)):
-            if not args[i]:
+            if not args[i]:  # test that input recieved data
                 self.AddRuntimeMessage(
                     Warning, "Input parameter {} failed to collect data.".format(joint_options.beam_names[i])
                 )
                 create_rule = False
             else:
+                beam_args = []
                 if not isinstance(args[i], list):
-                    args[i] = [args[i]]
-                beams.append(args[i])
+                    beam_args = [args[i]]
+                beams.append(beam_args)
 
         if create_rule:
-            if len(beams[0]) != len(beams[1]):
+            if len(beams[0]) != len(beams[1]):  # test that beam list lengths match
                 self.AddRuntimeMessage(
                     Error,
                     "Number of items in {} and {} must match!".format(
diff --git a/src/compas_timber/ghpython/ghcomponent_helpers.py b/src/compas_timber/ghpython/ghcomponent_helpers.py
index 1bd192bda..d415d406f 100644
--- a/src/compas_timber/ghpython/ghcomponent_helpers.py
+++ b/src/compas_timber/ghpython/ghcomponent_helpers.py
@@ -1,5 +1,6 @@
 from Grasshopper.Kernel.GH_RuntimeMessageLevel import Remark
 from Grasshopper.Kernel.GH_RuntimeMessageLevel import Warning
+import Grasshopper
 
 
 def list_input_valid(component, Param, name):
@@ -24,7 +25,7 @@ def item_input_valid(component, Param, name):
     return False
 
 
-def add_GH_param(name, io):
+def add_GH_param(name, io, ghenv):
     assert io in ("Output", "Input")
     params = [param.NickName for param in getattr(ghenv.Component.Params, io)]
     if name not in params:
@@ -40,17 +41,18 @@ def add_GH_param(name, io):
         ghenv.Component.Params.OnParametersChanged()
 
 
-def clear_GH_params(permanent_param_count = 1):
-    for param in ghenv.Component.Params.Input:
-        if param.Index >= permanent_param_count:
-            ghenv.Component.Params.UnregisterInputParameter(param)
+def clear_GH_params(ghenv, permanent_param_count=1):
+    while len(ghenv.Component.Params.Input) > permanent_param_count:
+        ghenv.Component.Params.UnregisterInputParameter(
+            ghenv.Component.Params.Input[len(ghenv.Component.Params.Input) - 1]
+        )
     ghenv.Component.Params.OnParametersChanged()
     ghenv.Component.ExpireSolution(False)
 
 
-def manage_dynamic_params(input_names, permanent_param_count = 1):
+def manage_dynamic_params(input_names, ghenv, permanent_param_count=1):
     if not input_names:  # if no joint_options is input
-        clear_GH_params(permanent_param_count)
+        clear_GH_params(ghenv, permanent_param_count)
         return
     register_params = False
     if len(ghenv.Component.Params.Input) == len(input_names) + permanent_param_count:
@@ -61,6 +63,6 @@ def manage_dynamic_params(input_names, permanent_param_count = 1):
     else:
         register_params = True
     if register_params:
-        clear_GH_params(permanent_param_count)
+        clear_GH_params(ghenv, permanent_param_count)
         for name in input_names:
-            add_GH_param(name, "Input")
+            add_GH_param(name, "Input", ghenv)
diff --git a/src/compas_timber/ghpython/workflow.py b/src/compas_timber/ghpython/workflow.py
index d9869c4da..5a5344a58 100644
--- a/src/compas_timber/ghpython/workflow.py
+++ b/src/compas_timber/ghpython/workflow.py
@@ -285,7 +285,7 @@ class JointOptions(object):
 
     """
 
-    def __init__(self, type, beam_names = [], **kwargs):
+    def __init__(self, type, beam_names=[], **kwargs):
         self.type = type
         self.kwargs = kwargs
         self.beam_names = beam_names