decrease memory used

src/main/java/com/alibaba/druid/proxy/jdbc/JdbcParameterNull.java

@@ -0,0 +1,33 @@
+package com.alibaba.druid.proxy.jdbc;
+
+import java.util.Calendar;
+
+public class JdbcParameterNull implements JdbcParameter {
+
+    private final int sqlType;
+
+    public JdbcParameterNull(int sqlType){
+        this.sqlType = sqlType;
+    }
+
+    @Override
+    public Object getValue() {
+        return null;
+    }
+
+    @Override
+    public long getLength() {
+        return 0;
+    }
+
+    @Override
+    public Calendar getCalendar() {
+        return null;
+    }
+
+    @Override
+    public int getSqlType() {
+        return sqlType;
+    }
+
+}