Update to code for null-safety.

[asartalo]

• updated dependencies to use null-safe versions
• updated code to use null-safe features

Fixes #2

[asartalo]

I've tried to limit the changes to what is only needed to support null-safety. I've only tested this on a local project and it seems to work.

One issue that I found while using the null-safe version is that the hooks will refuse to execute if some of the dependencies in the hooks themselves are not null-safe. This will undoubtedly break projects that haven't opted-in to null-safety.

[asartalo]

Hi @xuzhongpeng , do you need this PR to be in the develop branch and not master? Let me know if this is the case and other issues you see in my PR.

[xuzhongpeng]

Hi @xuzhongpeng , do you need this PR to be in the develop branch and not master? Let me know if this is the case and other issues you see in my PR.

I have reviewed the codes you pushed. It's running perfectly. But it is only fit SDK >=1.12.0-0 <3.0.0. I may push it in the future, but not now.

[asartalo]

Okay, no problem. It's up to you. :) Just want to let you know that any project that is marked as null-safe by pub.dev like http have to limit their sdk support that way. See http's pubspec.yaml as an example and the documentation on how to migrate packages to null-safety. If you need help with this I will gladly help but it's still up to you.

[xuzhongpeng]

Okay, no problem. It's up to you. :) Just want to let you know that any project that is marked as null-safe by pub.dev like http have to limit their sdk support that way. See http's pubspec.yaml as an example and the documentation on how to migrate packages to null-safety. If you need help with this I will gladly help but it's still up to you.

I have pulled your PR to nullSafety channel. I also have created a version 0.1.3-nullsafety.0 to pub.dev. Thank you for your code contribution.