Moving the code around so that each association type can customize it

src/ORM/Association.php

@@ -463,24 +463,6 @@ public function transformRow($row, $nestKey, $joined) {
 		return $row;
 	}
 
-/**
- * Returns a modified row after appending a property for this association
- * with the default empty value according to whether the association was
- * joined or fetched externally.
- *
- * @param array $row
- * @param boolean $joined Whether or not the row is a result of a direct join
- * with this association
- * @return array
- */
-	public function defaultRowValue($row, $joined) {
-		$sourceAlias = $this->source()->alias();
-		if (isset($row[$sourceAlias])) {
-			$row[$sourceAlias][$this->property()] = $joined ? null : [];
-		}
-		return $row;
-	}
-
 /**
  * Proxies the finding operation to the target table's find method
  * and modifies the query accordingly based of this association
@@ -703,4 +685,16 @@ public abstract function isOwningSide(Table $side);
  */
 	public abstract function save(Entity $entity, $options = []);
 
+/**
+ * Returns a modified row after appending a property for this association
+ * with the default empty value according to whether the association was
+ * joined or fetched externally.
+ *
+ * @param array $row
+ * @param boolean $joined Whether or not the row is a result of a direct join
+ * with this association
+ * @return array
+ */
+	abstract public function defaultRowValue($row, $joined);
+
 }

src/ORM/Association/BelongsTo.php

@@ -135,6 +135,18 @@ public function save(Entity $entity, $options = []) {
 		return $entity;
 	}
 
+/**
+ * {@inheritdoc}
+ *
+ */
+	public function defaultRowValue($row, $joined) {
+		$sourceAlias = $this->source()->alias();
+		if (isset($row[$sourceAlias])) {
+			$row[$sourceAlias][$this->property()] = null;
+		}
+		return $row;
+	}
+
 /**
  * Returns a single or multiple conditions to be appended to the generated join
  * clause for getting the results on the target table.

src/ORM/Association/ExternalAssociationTrait.php

@@ -77,6 +77,18 @@ public function sort($sort = null) {
 		return $this->_sort;
 	}
 
+/**
+ * {@inheritdoc}
+ *
+ */
+	public function defaultRowValue($row, $joined) {
+		$sourceAlias = $this->source()->alias();
+		if (isset($row[$sourceAlias])) {
+			$row[$sourceAlias][$this->property()] = $joined ? null : [];
+		}
+		return $row;
+	}
+
 /**
  * Returns the default options to use for the eagerLoader
  *

src/ORM/Association/HasOne.php

@@ -130,6 +130,18 @@ public function save(Entity $entity, $options = []) {
 		return $entity;
 	}
 
+/**
+ * {@inheritdoc}
+ *
+ */
+	public function defaultRowValue($row, $joined) {
+		$sourceAlias = $this->source()->alias();
+		if (isset($row[$sourceAlias])) {
+			$row[$sourceAlias][$this->property()] = null;
+		}
+		return $row;
+	}
+
 /**
  * {@inheritdoc}
  *

tests/TestCase/ORM/AssociationTest.php

@@ -52,7 +52,7 @@ public function setUp() {
 			'\Cake\ORM\Association',
 			[
 				'_options', 'attachTo', '_joinCondition', 'cascadeDelete', 'isOwningSide',
-				'save', 'eagerLoader', 'type'
+				'save', 'eagerLoader', 'type', 'defaultRowValue'
 			],
 			['Foo', $config]
 		);