Fix null value crash in postgresql_extensible input (#4689)

plugins/inputs/postgresql_extensible/postgresql_extensible_test.go

@@ -1,6 +1,7 @@
 package postgresql_extensible
 
 import (
+	"errors"
 	"fmt"
 	"testing"
 
@@ -223,3 +224,41 @@ func TestPostgresqlIgnoresUnwantedColumns(t *testing.T) {
 		assert.False(t, acc.HasMeasurement(col))
 	}
 }
+
+func TestAccRow(t *testing.T) {
+	p := Postgresql{}
+	var acc testutil.Accumulator
+	columns := []string{"datname", "cat"}
+
+	testRows := []fakeRow{
+		{fields: []interface{}{1, "gato"}},
+		{fields: []interface{}{nil, "gato"}},
+		{fields: []interface{}{"name", "gato"}},
+	}
+	for i := range testRows {
+		err := p.accRow("pgTEST", testRows[i], &acc, columns)
+		if err != nil {
+			t.Fatalf("Scan failed: %s", err)
+		}
+	}
+}
+
+type fakeRow struct {
+	fields []interface{}
+}
+
+func (f fakeRow) Scan(dest ...interface{}) error {
+	if len(f.fields) != len(dest) {
+		return errors.New("Nada matchy buddy")
+	}
+
+	for i, d := range dest {
+		switch d.(type) {
+		case (*interface{}):
+			*d.(*interface{}) = f.fields[i]
+		default:
+			return fmt.Errorf("Bad type %T", d)
+		}
+	}
+	return nil
+}