Fix getOption() calls to use empty string instead of null (#621)

Replace null with `''` in `SelectElement::getOption()`, since the placeholder
options for select elements are keyed by an empty string, not null.

Author: jrauh01

library/Vspheredb/Monitoring/Rule/RuleForm.php

@@ -170,7 +170,7 @@ protected function setInheritedValue($elementName, $value, $sourceName = null)
             } elseif ($optionValue === false) {
                 $optionValue = 'n';
             }
-            $element->getOption(null)->setContent(
+            $element->getOption('')->setContent(
                 implode(',', $element->getOption($optionValue)->getContent()) . $suffix
             );
         } elseif ($element instanceof TextElement || $element instanceof NumberElement) {

library/Vspheredb/Web/Form/InfluxDbConnectionForm.php

@@ -178,7 +178,7 @@ protected function appendVersionInformation($apiVersion, $detectedVersion)
         }
         $element = $this->getElement('api_version');
         assert($element instanceof SelectElement);
-        $autoOption = $element->getOption(null);
+        $autoOption = $element->getOption('');
         $autoOption->setLabel(\sprintf(
             $this->translate('Autodetect: %s API, Version is %s'),
             $apiVersion,