Maven - for artifact the version cannot be empty

You need to inherit from Spring Boot's parent POM:

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>1.3.5.RELEASE</version>
</parent>

This parent POM declares lots of dependency versions for artifacts you might use on your projects, that way you don't need to specify it yourself.

From the docs:

Each release of Spring Boot provides a curated list of dependencies it supports. In practice, you do not need to provide a version for any of these dependencies in your build configuration as Spring Boot is managing that for you. When you upgrade Spring Boot itself, these dependencies will be upgraded as well in a consistent way.

See also:

• Getting Started - Building an Application with Spring Boot

The version is missing in the following plugin declaration:

        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
        </plugin>

Just add the version:

        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <version>1.3.5.RELEASE</version>
        </plugin>