FIX: Do nothing if no text is present

Author: mgxd

nipype/pipeline/engine/nodes.py

@@ -752,10 +752,11 @@ def _run_command(self, execute, copyfiles=True):
         if exc_tb:
             runtime = result.runtime
 
-            def _tab(field):
+            def _tab(text):
                 from textwrap import indent
-
-                return indent(field, '\t')
+                if not text:
+                    return ""
+                return indent(text, '\t')
 
             msg = f"Exception raised while executing Node {self.name}.\n\n"
             if hasattr(runtime, 'cmdline'):