lib: Add MissingParameterException::getParameter and ::setParameter ...

... for getting/setting the name of the missing parameter which caused the exception.

refs #8886

library/Icinga/Exception/MissingParameterException.php

@@ -8,4 +8,33 @@
  */
 class MissingParameterException extends IcingaException
 {
+    /**
+     * Name of the missing parameter
+     *
+     * @var string
+     */
+    protected $parameter;
+
+    /**
+     * Get the name of the missing parameter
+     *
+     * @return string
+     */
+    public function getParameter()
+    {
+        return $this->parameter;
+    }
+
+    /**
+     * Set the name of the missing parameter
+     *
+     * @param   string  $name
+     *
+     * @return  $this
+     */
+    public function setParameter($name)
+    {
+        $this->parameter = (string) $name;
+        return $this;
+    }
 }