feat: 添加列默认值为 null 值时，逻辑删除的构建。

mybatis-flex-core/src/main/java/com/mybatisflex/core/logicdelete/NullableColumnLogicDeleteProcessor.java

@@ -0,0 +1,51 @@
+/*
+ *  Copyright (c) 2022-2023, Mybatis-Flex (fuhai999@gmail.com).
+ *  <p>
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *  <p>
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *  <p>
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+package com.mybatisflex.core.logicdelete;
+
+import com.mybatisflex.core.dialect.IDialect;
+import com.mybatisflex.core.query.QueryColumn;
+import com.mybatisflex.core.query.QueryWrapper;
+import com.mybatisflex.core.table.TableInfo;
+
+/**
+ * 数据列默认值为 {@code null} 值的逻辑删除处理器。
+ *
+ * @author 王帅
+ * @since 2023-07-30
+ */
+public abstract class NullableColumnLogicDeleteProcessor extends AbstractLogicDeleteProcessor {
+
+    @Override
+    public String buildLogicNormalCondition(String logicColumn, TableInfo tableInfo, IDialect dialect) {
+        return dialect.wrap(logicColumn) + " IS NULL";
+    }
+
+    @Override
+    public void buildQueryCondition(QueryWrapper queryWrapper, TableInfo tableInfo) {
+        QueryColumn queryColumn = new QueryColumn(tableInfo.getSchema(), tableInfo.getTableName(), tableInfo.getLogicDeleteColumn());
+        queryWrapper.and(queryColumn.isNull());
+    }
+
+    /**
+     * 逻辑删除字段值为 {@code null} 表示数据未删除。
+     */
+    @Override
+    public Object getLogicNormalValue() {
+        return null;
+    }
+
+}