wallet: send OPENs to unspendable nullData address

lib/wallet/wallet.js

@@ -1091,9 +1091,6 @@ class Wallet extends EventEmitter {
   async _importName(name) {
     const nameHash = rules.hashName(name);
 
-    if (await this.txdb.hasNameState(nameHash))
-      throw new Error('Name already exists.');
-
     const b = this.db.batch();
     await this.wdb.addNameMap(b, nameHash, this.wid);
     await b.write();
@@ -1561,7 +1558,17 @@ class Wallet extends EventEmitter {
     if (start !== 0 && start !== height)
       throw new Error('Name is already opening.');
 
-    const addr = await this.receiveAddress(acct);
+    // Send 0-value output to provably unspendable address:
+    // hs1lqqqqhuxwgy (mainnet) is the smallest valid nulldata address
+    // and represents witness version 31 folowed by data of 0x0000.
+    // Unspendable outputs do not bloat the UTXO set or the wallet's coin set.
+    const addr = Address.fromNulldata(Buffer.alloc(2));
+
+    // Since this address is not in our wallet, we must "manually" add the name
+    // to the wallet database's name map. Normally the wallet would do this in
+    // txdb.js connectNames() when a TX is inserted into the DB, and the wallet
+    // recognizes the output address.
+    await this.importName(name);
 
     const output = new Output();
     output.address = addr;