Check frequency option is present.

Closes #125.

Author: tobie

index.bs

@@ -717,7 +717,7 @@ Abstract Operations {#abstract-operations}
         1.  associate |sensor_instance| with |sensor|.
     1.  Otherwise, [=throw=] a TypeError.
     1.  Let |frequency| be the value of the {{frequency!!dict-member}} member of |options|.
-    1.  If |frequency| is not `null`,
+    1.  If |frequency| is [=present=],
         1.  If |sensor| [=supports periodic reporting mode=],
             1.  Set |sensor_instance|'s [=desired frequency=] to |frequency|.
         1.  Otherwise,

index.html

      <li data-md="">
       <p>Let <var>frequencyvar> be the value of the <code class="idl"><a class="idl-code" data-link-type="dict-member" href="#dom-sensoroptions-frequency" id="ref-for-dom-sensoroptions-frequency-1">frequencya>code> member of <var>optionsvar>.p>
      <li data-md="">
-      <p>If <var>frequencyvar> is not <code>nullcode>,p>
+      <p>If <var>frequencyvar> is <a data-link-type="dfn" href="https://heycam.github.io/webidl/#dfn-present">presenta>,p>
       <ol>
        <li data-md="">
         <p>If <var>sensorvar> <a data-link-type="dfn" href="#supports-periodic-reporting-mode" id="ref-for-supports-periodic-reporting-mode-1">supports periodic reporting modea>,p>
      <li><a href="https://heycam.github.io/webidl/#SecureContext">SecureContexta>
      <li><a href="https://heycam.github.io/webidl/#dfn-create-exception">createda>
      <li><a href="https://heycam.github.io/webidl/#dfn-exception">exceptiona>
+     <li><a href="https://heycam.github.io/webidl/#dfn-present">presenta>
      <li><a href="https://heycam.github.io/webidl/#dfn-throw">throwa>
     ul>
   ul>