not consistent with encoding/json when marshalling struct field with "omitempty" tag

[liuq19]

code

type Struct struct {
    F1   struct{ F2 string} `json:",omitempty"`
}
func TestMarshalStructFieldWithOmitemptyTag(t *testing.T) {
    var obj Struct

    out, err := Marshal(obj)
    require.NoError(t, err)

    want, err := json.Marshal(obj)
    require.NoError(t, err)

    require.Equal(t, string(want), string(out))
}

output

        	Error:      	Not equal:
        	            	expected: "{\"F1\":{\"F2\":\"\"}}"
        	            	actual  : "{}"

        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1 +1 @@
        	            	-{"F1":{"F2":""}}
        	            	+{}
        	Test:       	TestMarshalStructFieldWithOmitemptyTag