Fix get value of last column with same name in result rows (#3063)

* Add failing test for result rows with the same column names

* Fix handling of duplicate column names in results to ensure last value is populated

Fixes handling of result rows that have the same column name duplicated in the results to ensure
that the last value is the one returned to the user. This was the old behavior but unintentionally
broken when the pre-built object optimization was added.

packages/pg/lib/result.js

@@ -67,6 +67,8 @@ class Result {
       var field = this.fields[i].name
       if (rawValue !== null) {
         row[field] = this._parsers[i](rawValue)
+      } else {
+        row[field] = null
       }
     }
     return row

packages/pg/test/integration/gh-issues/3062-tests.js

@@ -0,0 +1,21 @@
+'use strict'
+const helper = require('../test-helper')
+var assert = require('assert')
+const suite = new helper.Suite()
+
+// https://github.com/brianc/node-postgres/issues/3062
+suite.testAsync('result fields with the same name should pick the last value', async () => {
+  const client = new helper.pg.Client()
+  await client.connect()
+
+  const { rows: [shouldBeNullRow] } = await client.query('SELECT NULL AS test, 10 AS test, NULL AS test')
+  assert.equal(shouldBeNullRow.test, null)
+
+  const { rows: [shouldBeTwelveRow] } = await client.query('SELECT NULL AS test, 10 AS test, 12 AS test')
+  assert.equal(shouldBeTwelveRow.test, 12)
+
+  const { rows: [shouldBeAbcRow] } = await client.query(`SELECT NULL AS test, 10 AS test, 12 AS test, 'ABC' AS test`)
+  assert.equal(shouldBeAbcRow.test, 'ABC')
+
+  await client.end()
+})