ORA-31670
        Username argument must be specified and non-null.
        
        
        Cause
        Called change user with a NULL username or a null string.
        Action
        Specify a valid username argument. If this error occurs from a Data Pump client (e.g. expdp or impdp), try the operation again. If the error occurs again, contact Oracle Customer Support and report the error.
        
     
    
    
        ORA-31670
        Username argument must be specified and non-null.
        
        
        Cause
        Called change user with a NULL username or a null string.
        Action
        Specify a valid username argument. If this error occurs from a Data Pump client (e.g. expdp or impdp), try the operation again. If the error occurs again, contact Oracle Customer Support and report the error.
        
     
    
    
        ORA-31670
        Username argument must be specified and non-null.
        
        
        Cause
        Called change user with a NULL username or a null string.
        Action
        Specify a valid username argument. If this error occurs from a Data Pump client (e.g. expdp or impdp), try the operation again. If the error occurs again, contact Oracle Customer Support and report the error.