How can I justify a technology over another? (Java over .NET)

Question

We are working in a Java/.NET company and my team and I are planning a project for a client.

One of the requirements is that the project has to be done in .NET

I've asked about this requirement, and the client said that it doesn't matter, and that if I have a good reason we can use other technology. But, I have to justify the decision.

As a Project Manager / Analyst I'm interested in making the project in Java because:

• The team knows java much better, regarding the language and frameworks
• I don't know anything about .NET technology (and maybe we could make bad decisions thinking in a Java way to do things)
• There are other people in company that have more skills in .NET but they have other projects with more priority.

For experience, I'm sure that if we use Java, the project will have much more quality. But this arguments could be weak from the client perspective.

How can I justify making the project in Java?

EDIT: I'm not asking if one technology is better than other. "It's not a technology war" question.