with date sharding rule, if sBeginDate is ommitted, do reload will get NPE

[irene-coming]

• dble version：
  5.6.29-dble-9.9.9.9-23d8c57-20180722154703
• preconditions ：
  sharding rule is not used by any table
• configs：

rule.xml

          <tableRule name="date_rule">
              <rule>
                  <columns>id</columns>
                  <algorithm>date_func</algorithm>
              </rule>
          </tableRule>
          <function class="Date" name="date_func">
              <property name="dateFormat">yyyy-MM-dd</property>
              <property name="sEndDate">2018-01-31</property>
              <property name="sPartionDay">10</property>
          </function>

• steps：
  step1. execute manager command: reload @@config_all

• expect result：

  1. give messages like 'sBeginDate is not found'

• real result：

  1. The reason is com.actiontech.dble.config.util.ConfigException: java.lang.NullPointerException

• supplements：
  1.

/label ~BUG

[irene-coming]

verfied on version: 5.6.29-dble-9.9.9.9-36b8e8b-20180820072207