Use internal Nullable annotation, allow drop sisu-inject from runtime dependencies

org.eclipse.sisu.inject is not exported by Maven Core ...
so plugins must add it to own dependency only for this one annotation

Own implementation avoid such situation

Author: slawekjaranowski

pom.xml

@@ -73,11 +73,12 @@ limitations under the License.
       <version>1</version>
       <scope>provided</scope>
     </dependency>
+
     <dependency>
       <groupId>org.eclipse.sisu</groupId>
       <artifactId>org.eclipse.sisu.inject</artifactId>
       <version>0.9.0.M4</version>
-      <scope>provided</scope>
+      <scope>test</scope>
     </dependency>
 
     <dependency>

src/main/java/org/codehaus/plexus/velocity/internal/DefaultVelocityComponent.java

@@ -25,7 +25,6 @@
 import org.apache.velocity.app.VelocityEngine;
 import org.codehaus.plexus.velocity.VelocityComponent;
 import org.codehaus.plexus.velocity.VelocityComponentConfigurator;
-import org.eclipse.sisu.Nullable;
 
 /**
  * Default component implementation. The presence of {@link VelocityComponentConfigurator} is optional.

src/main/java/org/codehaus/plexus/velocity/internal/Nullable.java

@@ -0,0 +1,18 @@
+package org.codehaus.plexus.velocity.internal;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Internal <code>Nullable</code> annotation to mark parameters that can be null.
+ * <p>
+ * Guice allow any Nullable annotation, so this one can be used instead of adding a dependency to sisu-inject.
+ * <a href="https://github.com/google/guice/wiki/UseNullable">UseNullable</a>
+ */
+@Target({ElementType.PARAMETER})
+@Retention(RetentionPolicy.RUNTIME)
+@Documented
+@interface Nullable {}