diff --git a/src/Models/Model.php b/src/Models/Model.php
index 1eb9a3f..5ddc042 100644
--- a/src/Models/Model.php
+++ b/src/Models/Model.php
@@ -124,6 +124,31 @@ public function getOriginal( string $key = null ) {
 		return $key ? $this->original[ $key ] : $this->original;
 	}
 
+	/**
+	 * Whether the property is set or not. This is different from isset() because this considers a `null` value as
+	 * being set. Defaults are considered set as well.
+	 *
+	 * @unreleased
+	 *
+	 * @return boolean
+	 */
+	public function isSet( string $key ): bool {
+		return array_key_exists( $key, $this->attributes ) || $this->hasDefault( $key );
+	}
+
+	/**
+	 * Check if there is a default value for a property.
+	 *
+	 * @unreleased
+	 *
+	 * @param string $key Property name.
+	 *
+	 * @return bool
+	 */
+	protected function hasDefault( string $key ): bool {
+		return is_array( $this->properties[ $key ] ) && array_key_exists( 1, $this->properties[ $key ] );
+	}
+
 	/**
 	 * Returns the default value for a property if one is provided, otherwise null.
 	 *
@@ -134,9 +159,11 @@ public function getOriginal( string $key = null ) {
 	 * @return mixed|null
 	 */
 	protected function getPropertyDefault( string $key ) {
-		return is_array( $this->properties[ $key ] ) && isset( $this->properties[ $key ][1] )
-			? $this->properties[ $key ][1]
-			: null;
+		if ( $this->hasDefault( $key ) ) {
+			return $this->properties[ $key ][1];
+		}
+
+		return null;
 	}
 
 	/**
@@ -149,7 +176,9 @@ protected function getPropertyDefault( string $key ) {
 	protected function getPropertyDefaults() : array {
 		$defaults = [];
 		foreach ( array_keys( $this->properties ) as $property ) {
-			$defaults[ $property ] = $this->getPropertyDefault( $property );
+			if ( $this->hasDefault( $property ) ) {
+				$defaults[ $property ] = $this->getPropertyDefault( $property );
+			}
 		}
 
 		return $defaults;
diff --git a/tests/wpunit/ModelTest.php b/tests/wpunit/ModelTest.php
index b8e05c8..1adf2e4 100644
--- a/tests/wpunit/ModelTest.php
+++ b/tests/wpunit/ModelTest.php
@@ -277,6 +277,25 @@ public function testShouldSetMultipleAttributes() {
 		$this->assertEquals( 'Skywalker', $model->lastName );
 	}
 
+	/**
+	 * @unreleased
+	 *
+	 * @return void
+	 */
+	public function testIsSet() {
+		$model = new MockModel();
+
+		// This has a default so we should see as set.
+		$this->assertTrue( $model->isSet( 'firstName' ) );
+
+		// No default, and hasn't been set so show false.
+		$this->assertFalse( $model->isSet( 'lastName' ) );
+
+		// Now we set it, so it should be true - even though we set it to null.
+		$model->lastName = null;
+		$this->assertTrue( $model->isSet( 'lastName' ) );
+	}
+
 	/**
 	 * @since 1.0.0
 	 *