[xdata] Add BooleanFormField.getValueAsBooleanOrNull()

This method is meant to provide 'raw' access to what has been sent
over the wire. It is assumed to be not of much use in the typically
case, but provided for completeness.

smack-extensions/src/main/java/org/jivesoftware/smackx/xdata/BooleanFormField.java

@@ -49,6 +49,20 @@ public class BooleanFormField extends SingleValueFormField {
         return value;
     }
 
+    /**
+     * Get the value of the boolean field or maybe <code>null</code>. Note that you usually want to use
+     * {@link #getValueAsBoolean()} instead of this method, as {@link #getValueAsBoolean()} considers the default value
+     * of boolean fields. That is, boolean form fields have the value <code>false</code> if not explicitly set to
+     * something else.
+     *
+     * @return the boolean value of this form field or <code>null</code> if no value was explicitly provided.
+     * @see #getValueAsBoolean()
+     * @since 4.4.5
+     */
+    public Boolean getValueAsBooleanOrNull() {
+        return value;
+    }
+
     public Builder asBuilder() {
         return new Builder(this);
     }