Fix: unused parenthesis for parameters of FunctionExpression.

src/Database/Expression/FunctionExpression.php

@@ -127,7 +127,7 @@ class FunctionExpression extends QueryExpression
         $parts = [];
         foreach ($this->_conditions as $condition) {
             if ($condition instanceof ExpressionInterface) {
-                $condition = $condition->sql($generator);
+                $condition = sprintf('(%s)', $condition->sql($generator));
             } elseif (is_array($condition)) {
                 $p = $generator->placeholder('param');
                 $generator->bind($p, $condition['value'], $condition['type']);