obi uniq: better error checking

python/obitools3/commands/uniq.pyx

@@ -481,15 +481,17 @@ def run(config):
     
     logger("info","obi uniq")
     
+    # Open the input
     input = open_uri(config['obi']['inputURI'])
-    
+    if input is None:
+        raise Exception("Could not read input view")    
     if input[2] != View_NUC_SEQS:
         raise NotImplementedError('obi uniq only works on NUC_SEQS views')
     
+    # Open the output
     output = open_uri(config['obi']['outputURI'],
                       input=False,
                       newviewtype=View_NUC_SEQS)
-    
     if output is None:
         raise Exception("Could not create output view")