|   | 1 |  initial version  | 
Thank you for the report. This is a bug with sparse matrices, which is now tracked at #28935.
As a workaround, you could use:
sage: diagonal_matrix([0], sparse=False).exp()
[1]
 Copyright Sage, 2010. Some rights reserved under creative commons license. Content on this site is licensed under a Creative Commons Attribution Share Alike 3.0 license.
 
                
                Copyright Sage, 2010. Some rights reserved under creative commons license. Content on this site is licensed under a Creative Commons Attribution Share Alike 3.0 license.