Describe the bug
Front-end post empty string strategy value in timeout params, and the master and worker will produce the com.fasterxml.jackson.databind.exc.InvalidFormatException because of the enum type of strategy.

To Reproduce

1. Create a new simple shell process definition in front-end.
2. I just fill the name and code of shell node, do not fill or select the other options.
3. Save the process definition and your will find out the front-end post the wrong empty string strategy in timeout of processDefinitionJson.
   4.When you run the process definition, then master and worker will serde the processDefinitionJson to object, it will produce com.fasterxml.jackson.databind.exc.InvalidFormatException because of the enum type of strategy.

Expected behavior
Front-end post empty string strategy value in timeout params.

Screenshots

Which version of Dolphin Scheduler:
-[dev]

**Requirement or improvement

• Fix the timeout strategy value when front-end post to the back-end or change enum serde of strategy.