Better docs on the Extensions

Signed-off-by: Francesco Guardiani <francescoguard@gmail.com>

Author: slinkydeveloper

api/src/main/java/io/cloudevents/CloudEventExtensions.java

@@ -34,7 +34,7 @@ public interface CloudEventExtensions {
      * Get the extension attribute named {@code extensionName}
      *
      * @param extensionName the extension name
-     * @return the extension value or null if this instance doesn't contain such extension
+     * @return the extension value in one of the valid types String/Number/Boolean or null if this instance doesn't contain such extension
      */
     @Nullable
     Object getExtension(String extensionName);

api/src/main/java/io/cloudevents/Extension.java

@@ -29,17 +29,17 @@
 public interface Extension {
 
     /**
-     * Fill this materialized extension with values from a {@link CloudEventExtensions} implementation
+     * Fill this materialized extension with values from a {@link CloudEventExtensions} implementation.
      *
-     * @param extensions
+     * @param extensions the extensions where to read from
      */
     void readFrom(CloudEventExtensions extensions);
 
     /**
-     * Get the attribute of extension named {@code key}
+     * Get the attribute of extension named {@code key}.
      *
      * @param key the name of the extension attribute
-     * @return the extension value
+     * @return the extension value in one of the valid types String/Number/Boolean
      * @throws IllegalArgumentException if the key is unknown to this extension
      */
     @Nullable