When dealing with an explicit target on definition search. First test…

… for implemtnations which have a non-empty target string.

If not found then fallback to non-target implementations.
This should fix returning non-target implementations before trying to find implementations with targets.

source/MaterialXCore/Definition.cpp

@@ -72,17 +72,28 @@ InterfaceElementPtr NodeDef::getImplementation(const string& target) const
     const TargetDefPtr targetDef = getDocument()->getTargetDef(target);
     const StringVec candidateTargets = targetDef ? targetDef->getMatchingTargets() : StringVec();
 
-    // Search the candidate targets in order
+    // Search the candidate targets in inheritance order
     for (const string& candidateTarget : candidateTargets)
     {
         for (InterfaceElementPtr interface : interfaces)
         {
-            if (targetStringsMatch(interface->getTarget(), candidateTarget))
+            const std::string& interfaceTarget = interface->getTarget();
+            if (!interfaceTarget.empty() && targetStringsMatch(interfaceTarget, candidateTarget))
             {
                 return interface;
             }
         }
     }
+    // If no exact target match is found then return the first interface without a target
+    for (InterfaceElementPtr interface : interfaces)
+    {
+        // Look for interfaces without targets
+        const std::string& interfaceTarget = interface->getTarget();
+        if (interfaceTarget.empty())
+        {
+            return interface;
+        }
+    }
 
     return InterfaceElementPtr();
 }