Use isEmpty() method instead of empty() function

Closes #3301390

src/Plugin/FieldInheritance/FieldInheritancePluginBase.php

@@ -221,21 +221,24 @@ abstract class FieldInheritancePluginBase extends PluginBase implements FieldInh
   /**
    * Retrieve inherited data.
    *
-   * @return string
+   * @return array
    *   The inherited data.
    */
   protected function inheritData() {
     $source_entity = $this->getSourceEntity();
-    if ($source_entity === FALSE) {
+    if ($source_entity === FALSE
+      || $source_entity->{$this->getSourceField()}->isEmpty()
+    ) {
       return [];
     }
-    return $source_entity->{$this->getSourceField()}->getValue() ?? '';
+
+    return $source_entity->{$this->getSourceField()}->getValue();
   }
 
   /**
    * Retrieve prepended data.
    *
-   * @return string
+   * @return array
    *   The prepended data.
    */
   protected function prependData() {
@@ -247,10 +250,10 @@ abstract class FieldInheritancePluginBase extends PluginBase implements FieldInh
       return $values;
     }
 
-    if (!empty($destination_entity->{$this->getDestinationField()}->getValue())) {
+    if (!$destination_entity->{$this->getDestinationField()}->isEmpty()) {
       $values = array_merge($values, $destination_entity->{$this->getDestinationField()}->getValue());
     }
-    if (!empty($source_entity->{$this->getSourceField()}->getValue())) {
+    if (!$source_entity->{$this->getSourceField()}->isEmpty()) {
       $values = array_merge($values, $source_entity->{$this->getSourceField()}->getValue());
     }
     return $values;
@@ -271,10 +274,10 @@ abstract class FieldInheritancePluginBase extends PluginBase implements FieldInh
       return $values;
     }
 
-    if (!empty($source_entity->{$this->getSourceField()}->getValue())) {
+    if (!$source_entity->{$this->getSourceField()}->isEmpty()) {
       $values = array_merge($values, $source_entity->{$this->getSourceField()}->getValue());
     }
-    if (!empty($destination_entity->{$this->getDestinationField()}->getValue())) {
+    if (!$destination_entity->{$this->getDestinationField()}->isEmpty()) {
       $values = array_merge($values, $destination_entity->{$this->getDestinationField()}->getValue());
     }
     return $values;
@@ -283,7 +286,7 @@ abstract class FieldInheritancePluginBase extends PluginBase implements FieldInh
   /**
    * Retrieve fallback data.
    *
-   * @return string
+   * @return array
    *   The fallback data.
    */
   protected function fallbackData() {
@@ -295,10 +298,10 @@ abstract class FieldInheritancePluginBase extends PluginBase implements FieldInh
       return $values;
     }
 
-    if (!empty($destination_entity->{$this->getDestinationField()}->getValue())) {
+    if (!$destination_entity->{$this->getDestinationField()}->isEmpty()) {
       $values = $destination_entity->{$this->getDestinationField()}->getValue();
     }
-    elseif (!empty($source_entity->{$this->getSourceField()}->getValue())) {
+    elseif (!$source_entity->{$this->getSourceField()}->isEmpty()) {
       $values = $source_entity->{$this->getSourceField()}->getValue();
     }
     return $values;