Gin binding time.Time with empty value returns error

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Description

Binding query parameter to time.Time field,when query parameter is a zero value, ShouldBind returns error.

How to reproduce

package main

import (
    "github.com/gin-gonic/gin"
)

func main() {
    g := gin.Default()
    g.GET("/", func(c *gin.Context) {
        var req struct {
            CreatedAt time.Time `form:"created_at" time_format:"unix"`
        }
        if err := c.ShouldBind(&req); err != nil {
            str := fmt.Sprintf("\n======err:%v\n", err)
            c.String(200, str)
            return
        }
        c.String(200, req.CreatedAt.String())
    })
    g.Run(":9000")
}

Expectations

$ curl "http://localhost:9000/?created_at="
1970-01-01 08:00:00 +0800 CST

Actual result

$ curl "http://localhost:9000/?created_at="
======err:strconv.ParseInt: parsing "": invalid syntax
0001-01-01 00:00:00 +0000 UTC

Environment

• go version: go version go1.23.0 darwin/arm64
• gin version (or commit ref): 1.9.1
• operating system: mac m2

I think these lines of code should move up to function start https://github.com/gin-gonic/gin/blob/e46bd521859fdfc83c508f1d42c92cb7f91e9fcb/binding/form_mapping.go#L417-L420