Use empty string to disable version (#512)

Fixes #508.

src/docs/configuration/README.md

@@ -14,10 +14,10 @@ details.
 ## Configuring Output Name
 
 Shadow configures the default `shadowJar` task to set the output JAR's `destinationDir`, `baseName`, `appendix`,
-`version`, and `extension` to the same default values as Gradle does for all `Jar` tasks.
+`archiveVersion`, and `extension` to the same default values as Gradle does for all `Jar` tasks.
 Additionally, it configures the `classifier` to be `all`.
 
-If working with a Gradle project with the name `myApp` and version `1.0`, the default `shadowJar` task will output a
+If working with a Gradle project with the name `myApp` and archiveVersion `1.0`, the default `shadowJar` task will output a
 file at: `build/libs/myApp-1.0-all.jar`
 
 As with all `Jar` tasks in Gradle, these values can be overridden:
@@ -26,8 +26,8 @@ As with all `Jar` tasks in Gradle, these values can be overridden:
 // Output to build/libs/shadow.jar
 shadowJar {
    baseName = 'shadow'
-   classifier = null
-   version = null
+   classifier = ''
+   archiveVersion = ''
 }
 ```