[ISSUE #10207] Fix potential NPE in HA connections when remote address is null

[daguimu]

Problem

In DefaultHAConnection and AutoSwitchHAConnection, .toString() is called directly on the return value of getRemoteSocketAddress() without a null check:

this.clientAddress = this.socketChannel.socket().getRemoteSocketAddress().toString();

Socket.getRemoteSocketAddress() returns null if the socket is not connected. Under network instability (e.g., slave connects and immediately disconnects before the HA connection constructor completes), this throws NullPointerException.

Root Cause

No null check on the return value of getRemoteSocketAddress() before calling .toString().

Fix

Extract the SocketAddress into a local variable and check for null before calling .toString():

SocketAddress remoteAddress = this.socketChannel.socket().getRemoteSocketAddress();
this.clientAddress = remoteAddress != null ? remoteAddress.toString() : "";

Applied to both:

• DefaultHAConnection.java:64
• AutoSwitchHAConnection.java:109

Tests Added

• testConstructorWithNullRemoteAddress — Creates a DefaultHAConnection with a non-connected SocketChannel (where getRemoteSocketAddress() returns null). Verifies no NPE is thrown and clientAddress is set to empty string.

Impact

• Defensive null check only, no behavioral change for normal connected sockets
• Prevents NPE crash during HA connection setup under network instability

Fixes #10207