Format nil time.Time's without panicking

Fixes #82

Updates the DateFormat function to return an empty string if the
provided `*time.Time` is `nil`, instead of panicking.

Author: bentranter

app/utils/date.go

@@ -56,6 +56,10 @@ var conversion = map[rune]string{
 //		%z		numbers representing the timezone, ex: "-0700"
 //		%L		milliseconds, ex: ".000"
 func DateFormat(t *time.Time, format string) string {
+	if t == nil {
+		return ""
+	}
+
 	retval := make([]byte, 0, len(format))
 	for i, ni := 0, 0; i < len(format); i = ni + 2 {
 		ni = strings.IndexByte(format[i:], '%')

app/utils/date_test.go

@@ -2,9 +2,10 @@ package utils
 
 import (
 	"fmt"
-	. "github.com/smartystreets/goconvey/convey"
 	"testing"
 	"time"
+
+	. "github.com/smartystreets/goconvey/convey"
 )
 
 func ExampleDateFormat() {
@@ -22,4 +23,11 @@ func TestDateFormat(t *testing.T) {
 			So(dateFmt, ShouldEqual, "2009-11-10 23:00")
 		})
 	})
+
+	Convey("It should not panic when trying to format nil dates", t, func() {
+		dateFmt := DateFormat(nil, "%Y-%m-%d %H:%M")
+		Convey("Test DateFormat", func() {
+			So(dateFmt, ShouldEqual, "")
+		})
+	})
 }