Fix ContextValue validation in the AP

Author: zml2008

src/ap/java/org/spongepowered/plugin/processor/ListenerParameterAnnotation.java

@@ -63,7 +63,7 @@ void validate(final ParameterContext ctx) {
                     if (!contained.getModifiers().contains(Modifier.STATIC)) {
                         ctx.logError("The @ContextValue annotation must refer to a static field", entry.getValue());
                     }
-                    if (!ctx.types().isSubtype(contained.asType(), key.asType())) {
+                    if (!ctx.types().isSubtype(contained.asType(), ctx.types().erasure(key.asType()))) {
                         ctx.logError("The @ContextValue annotation must refer to a field with type EventContextKey, but got '" + contained.asType() + "' instead", entry.getValue());
                     }
                     // validate field type?

src/main/java/org/spongepowered/api/event/filter/cause/ContextValue.java

@@ -26,6 +26,7 @@
 
 import org.spongepowered.api.event.EventContext;
 import org.spongepowered.api.event.EventContextKey;
+import org.spongepowered.api.event.EventContextKeys;
 
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
@@ -46,6 +47,8 @@
     /**
      * Gets the name to use with the {@link EventContextKey}.
      *
+     * <p>This must be a field in {@link EventContextKeys}.</p>
+     *
      * @return The name to use
      */
     String value();