From 4744c8d560418e8ed7332252775d07862817424b Mon Sep 17 00:00:00 2001
From: Patrick Macdonald <4705216+reformstudios@users.noreply.github.com>
Date: Fri, 31 Jul 2020 10:37:13 +0100
Subject: [PATCH] Fix for error when getting sgtk alembic nodes.

The following methods are failing :-
hou.nodeType(hou.ropNodeTypeCategory(), tk_node_type).instances()
hou.nodeType(hou.sopNodeTypeCategory(), tk_node_type).instances()

This is because if there are no nodes of that type, the first part of the line returns None, and raises an error as it has no "instances()" method.

The nodes need to be gathered first, and if there are are any, THEN get their instances.
---
 python/tk_houdini_alembicnode/handler.py | 56 ++++++++++++++----------
 1 file changed, 33 insertions(+), 23 deletions(-)

diff --git a/python/tk_houdini_alembicnode/handler.py b/python/tk_houdini_alembicnode/handler.py
index 60dea3e..5881879 100644
--- a/python/tk_houdini_alembicnode/handler.py
+++ b/python/tk_houdini_alembicnode/handler.py
@@ -81,16 +81,18 @@ def convert_back_to_tk_alembic_nodes(cls, app):
 
         # get all rop/sop alembic nodes in the session
         alembic_nodes = []
-        alembic_nodes.extend(
-            hou.nodeType(
-                hou.sopNodeTypeCategory(), cls.HOU_SOP_ALEMBIC_TYPE
-            ).instances()
-        )
-        alembic_nodes.extend(
-            hou.nodeType(
-                hou.ropNodeTypeCategory(), cls.HOU_ROP_ALEMBIC_TYPE
-            ).instances()
-        )
+        
+        sop_nodes = hou.nodeType(hou.sopNodeTypeCategory(), cls.HOU_SOP_ALEMBIC_TYPE)
+        rop_nodes = hou.nodeType(hou.ropNodeTypeCategory(), cls.HOU_ROP_ALEMBIC_TYPE)
+        
+        if sop_nodes:
+            alembic_nodes.extend(
+                sop_nodes.instances()
+            )
+        if rop_nodes:
+            alembic_nodes.extend(
+                rop_nodes.instances()
+            )
 
         if not alembic_nodes:
             app.log_debug("No Alembic Nodes found for conversion.")
@@ -190,12 +192,16 @@ def convert_to_regular_alembic_nodes(cls, app):
 
         # get all instances of tk alembic rop/sop nodes
         tk_alembic_nodes = []
-        tk_alembic_nodes.extend(
-            hou.nodeType(hou.sopNodeTypeCategory(), tk_node_type).instances()
-        )
-        tk_alembic_nodes.extend(
-            hou.nodeType(hou.ropNodeTypeCategory(), tk_node_type).instances()
-        )
+        sop_nodes = hou.nodeType(hou.sopNodeTypeCategory(), tk_node_type)
+        rop_nodes = hou.nodeType(hou.ropNodeTypeCategory(), tk_node_type)
+        if sop_nodes:
+            tk_alembic_nodes.extend(            
+                sop_nodes.instances()
+            )
+        if rop_nodes:
+            tk_alembic_nodes.extend(
+                rop_nodes.instances()
+            )
 
         if not tk_alembic_nodes:
             app.log_debug("No Toolkit Alembic Nodes found for conversion.")
@@ -278,13 +284,17 @@ def get_all_tk_alembic_nodes(cls):
 
         # get all instances of tk alembic rop/sop nodes
         tk_alembic_nodes = []
-        tk_alembic_nodes.extend(
-            hou.nodeType(hou.sopNodeTypeCategory(), tk_node_type).instances()
-        )
-        tk_alembic_nodes.extend(
-            hou.nodeType(hou.ropNodeTypeCategory(), tk_node_type).instances()
-        )
-
+        sop_nodes = hou.nodeType(hou.sopNodeTypeCategory(), tk_node_type)
+        rop_nodes = hou.nodeType(hou.ropNodeTypeCategory(), tk_node_type)
+        if sop_nodes:
+            tk_alembic_nodes.extend(            
+                sop_nodes.instances()
+            )
+        if rop_nodes:
+            tk_alembic_nodes.extend(
+                rop_nodes.instances()
+            )
+            
         return tk_alembic_nodes
 
     @classmethod