Fix nullable docblock for mutator methods.

Author: dereuromark

src/Propel/Generator/Builder/Om/ObjectBuilder.php

@@ -1601,16 +1601,22 @@ public function addJsonMutatorComment(&$script, Column $column)
      *
      * @param string $script
      * @param Column $column
+     * @return void
      */
     public function addMutatorComment(&$script, Column $column)
     {
         $clo = $column->getLowercasedName();
+        $type = $column->getPhpType();
+        if ($type && !$column->isNotNull()) {
+            $type .= '|null';
+        }
+
         $script .= "
     /**
      * Set the value of [$clo] column.
-     * ".$column->getDescription()."
-     * @param ".($column->getPhpType() ?: 'mixed')." \$v new value
-     * @return \$this|".$this->getObjectClassName(true)." The current object (for fluent API support)
+     * " . $column->getDescription() . "
+     * @param " . $type . " \$v New value
+     * @return \$this|" . $this->getObjectClassName(true) . " The current object (for fluent API support)
      */";
     }