func (f *Float) UnmarshalJSON(data []byte) error {
	var err error
	var v interface{}
	json.Unmarshal(data, &v)
	switch x := v.(type) {
	case float64:
		f.Float64 = float64(x)
	case map[string]interface{}:
		err = json.Unmarshal(data, &f.NullFloat64)
	case nil:
		f.Valid = false
		return nil
	default:
		err = fmt.Errorf("json: cannot unmarshal %v into Go value of type null.Float", reflect.TypeOf(v).Name())
	}
	f.Valid = err == nil
	return err
}
UnmarshalJSON implements json.Unmarshaler.
It supports number and null input.
0 will not be considered a null Float.
It also supports unmarshalling a sql.NullFloat64.
package null
import (
	"database/sql"
	"encoding/json"
	"fmt"
	"reflect"
	"strconv"
)
type Float struct {
	sql.NullFloat64
}
func NewFloat(f float64, valid bool) Float {
	return Float{
		NullFloat64: sql.NullFloat64{
			Float64: f,
			Valid:   valid,
		},
	}
}
func FloatFrom(f float64) Float {
	return NewFloat(f, true)
}
func FloatFromPtr(f *float64) Float {
	if f == nil {
		return NewFloat(0, false)
	}
	return NewFloat(*f, true)
}