Result of calling rpc get-arp-table defined in misc-config.yang is false.

Branch: stable/beryllium.

There are three switches in my experiment, and their connections are as follows.
s1(GE1/0)-----(GE1/0)s2(GE2/0)-----(GE1/0)s3

File snmp4sdn_swdb.csv is as follows, and there are only s1 and s2 in this file.
MAC,IP,SNMP_Community,CLI_Username,CLI_Password,Model
74:25:8a:e4:11:be,17.0.2.104,public,admin,admin,H3C_VSR
74:25:8a:e3:56:b4,17.0.3.105,public,admin,admin,H3C_VSR

Firstly, I use command snmp4sdn:readdb to read device information about s1 and s2. The result is as follows.
MAC_address (sid) IP_address SNMP_community CLI_username CLI_password Model_name
=======================================================================
00:00:74:25:8a:e3:56:b4 (127704592766644 ) 17.0.3.105 public admin admin H3C_VSR
00:00:74:25:8a:e4:11:be (127704592814526 ) 17.0.2.104 public admin admin H3C_VSR
MAC_address (sid) IP_address SNMP_community CLI_username CLI_password Model_name
=======================================================================
00:00:74:25:8a:e3:56:b4 (127704592766644 ) 17.0.3.105 public admin admin H3C_VSR
00:00:74:25:8a:e4:11:be (127704592814526 ) 17.0.2.104 public admin admin H3C_VSR

Arp table on switch s1 is as follows.
IP address MAC address VLAN Interface Aging Type
17.0.0.105 000c-2961-ee6b N/A GE1/0 17 D
17.0.2.107 000c-2970-f2b2 N/A GE2/0 17 D

Then, I call rpc get-arp-table defined in file misc-config.yang to get the arp table on switch s1. But the output of this rpc is null.