Fix nil argument exceptions when clearing an empty session

- Resolves 'nil argument to function' exceptions in lambdas bound to
  before/after-graph-view-change events in mode_manager.mu, wipes.mu,
  and transform_manip.mu.
- Fixes rvc.frame() throwing exceptions on an empty session in
  multiple_source_media_rep.py and its utilities.
Signed-off-by: Michael Oliver <mcoliver@gmail.com>

Author: mcoliver

src/lib/app/mu_rvui/mode_manager.mu

@@ -751,17 +751,28 @@ class: ModeManagerMode : MinorMode
 
     method: viewChange (void; Event event, bool on)
     {
-        event.reject();
+        try 
+        {
+            event.reject();
 
-        let vnode = viewNode(),
-            vtype = nodeType(vnode),
-            name  = if vtype.substr(0,2) == "RV" then vtype.substr(2,0) + "_edit_mode" else "",
-            entry = findModeEntry(name);
+            let vnode = viewNode();
+            if (vnode eq nil || vnode == "") return;
 
-        if (entry neq nil)
-        {
-            activateEntry(entry, on);
-            if (on) sendInternalEvent("view-edit-mode-activated");
+            let vtype = nodeType(vnode);
+            if (vtype eq nil || vtype == "") return;
+
+            let name  = if vtype.substr(0,2) == "RV" then vtype.substr(2,0) + "_edit_mode" else "",
+                entry = findModeEntry(name);
+
+            if (entry neq nil)
+            {
+                activateEntry(entry, on);
+                if (on) sendInternalEvent("view-edit-mode-activated");
+            }
+        } 
+        catch (exception exc) 
+        { 
+            print("ERROR: mode_manager viewChange: " + string(exc) + "\\n"); 
         }
     }
 

src/lib/app/mu_rvui/wipes.mu

@@ -465,13 +465,22 @@ class: Wipe : MinorMode
     { 
         event.reject();
         removeTags(); 
-        set(viewNode() + ".ui.wipes", 1);
+        
+        let vnode = viewNode();
+        if (vnode neq nil && vnode != "")
+        {
+            set(vnode + ".ui.wipes", 1);
+        }
     }
 
     method: afterGraphViewChange (void; Event event) 
     { 
         event.reject();
-        if (nodeType(viewNode()) != "RVStackGroup")
+        
+        let vnode = viewNode();
+        if (vnode eq nil || vnode == "") return;
+        
+        if (nodeType(vnode) != "RVStackGroup")
         {
             toggle();
         }

src/plugins/rv-packages/multiple_source_media_rep/multiple_source_media_rep.py

@@ -441,7 +441,10 @@ def _update_media_info(self, event):
             return
 
         # Important: Skip update if same sources as current.
-        sources = rvc.sourcesAtFrame(rvc.frame())
+        try:
+            sources = rvc.sourcesAtFrame(rvc.frame())
+        except Exception:
+            sources = []
         if sources == self._current_sources and not self._force_update_media_info:
             return
 

src/plugins/rv-packages/multiple_source_media_rep/multiple_source_media_rep_utils.py

@@ -25,7 +25,10 @@ def get_source_at_current_frame():
     """
     Returns first source at current frame.
     """
-    sources = rvc.sourcesAtFrame(rvc.frame())
+    try:
+        sources = rvc.sourcesAtFrame(rvc.frame())
+    except Exception:
+        sources = []
     return "" if not sources else sources[0]
 
 
@@ -34,7 +37,10 @@ def get_switch_node(source):
     Retrieves the first RVSwitch node at current frame.
     """
     if source:
-        switch_nodes = rve.nodesInEvalPath(rvc.frame(), "RVSwitch", source)
+        try:
+            switch_nodes = rve.nodesInEvalPath(rvc.frame(), "RVSwitch", source)
+        except Exception:
+            switch_nodes = []
         if switch_nodes:
             return switch_nodes[0]
 
@@ -47,9 +53,16 @@ def get_switch_nodes_at_current_frame():
     """
     switch_nodes = []
 
-    sources = rvc.sourcesAtFrame(rvc.frame())
+    try:
+        sources = rvc.sourcesAtFrame(rvc.frame())
+    except Exception:
+        sources = []
+
     for source in sources:
-        src_switch_nodes = rve.nodesInEvalPath(rvc.frame(), "RVSwitch", source)
+        try:
+            src_switch_nodes = rve.nodesInEvalPath(rvc.frame(), "RVSwitch", source)
+        except Exception:
+            src_switch_nodes = []
         if src_switch_nodes:
             switch_nodes.append(src_switch_nodes[0])
 

src/plugins/rv-packages/session_manager/transform_manip.mu

@@ -338,9 +338,12 @@ class: TransformManip : MinorMode
 
     method: findEditingNodes (void; bool setStates=true)
     {
-        let vnode       = viewNode(),
-            infos       = metaEvaluateClosestByType(frame(), "RVTransform2D"),
-            (ins, outs) = nodeConnections(viewNode(), false);
+        let vnode       = viewNode();
+        if (vnode eq nil || vnode == "") return;
+        
+        // Use an explicit type declaration here so that infos is correctly MetaEvalInfo[]
+        let infos       = metaEvaluateClosestByType(frame(), "RVTransform2D"),
+            (ins, outs) = nodeConnections(vnode, false);
 
         _editNodes = EditNodePair[]();