Node has Parent context does not explicitly check if the field exists. (#1019)

* Check that the field exists on node

* Early exit with disabled check

src/IslandoraContextManager.php

@@ -37,7 +37,7 @@ class IslandoraContextManager extends ContextManager {
     }
     /** @var \Drupal\context\ContextInterface $context */
     foreach ($this->getContexts() as $context) {
-      if ($this->evaluateContextConditions($context, $provided) && !$context->disabled()) {
+      if (!$context->disabled() && $this->evaluateContextConditions($context, $provided)) {
         $this->activeContexts[$context->id()] = $context;
       }
     }

src/Plugin/Condition/NodeHasParent.php

@@ -137,9 +137,11 @@ class NodeHasParent extends ConditionPluginBase implements ContainerFactoryPlugi
    *   TRUE if entity references the specified parent.
    */
   protected function evaluateEntity(EntityInterface $entity) {
-    foreach ($entity->referencedEntities() as $referenced_entity) {
-      if ($entity->getEntityTypeID() == 'node' && $referenced_entity->getEntityTypeId() == 'node') {
     $parent_reference_field = $this->configuration['parent_reference_field'];
+    foreach ($entity->referencedEntities() as $referenced_entity) {
+      // Check whether the entity and the referenced entity are nodes.
+      // Also make sure that the field exists.
+      if ($entity->getEntityTypeID() == 'node' && $entity->hasField($parent_reference_field) && $referenced_entity->getEntityTypeId() == 'node') {
         $field = $entity->get($parent_reference_field);
         if (!$field->isEmpty()) {
           $nids = $field->getValue();