json.Marshal() and sheriff.Marshal() gives different results when empty map present in struct

[mandeepji]

When empty map is present in Structure sheriff.Marshal() gives nil but json.Marshal() gives empty json {}

I used existing test TestMarshal_EmptyMap and Marshal same object using json & sheriff and got different results.

Modified Test func:

func TestMarshal_EmptyMap(t *testing.T) {                   
        emp := EmptyMapTest{                                
                AMap: make(map[string]string),              
        }                                                   
        o := &Options{                                      
                Groups: []string{"test"},                   
        }                                                   
                                                            
        actualMap, err := Marshal(o, emp)                   
        assert.NoError(t, err)                              
                                                            
        actual, err := json.Marshal(actualMap)              
        assert.NoError(t, err)                              
                                                            
        expected, err := json.Marshal(emp)                  
        assert.NoError(t, err)                              
                                                            
        assert.Equal(t, string(expected), string(actual))   
}

Test result:

--- FAIL: TestMarshal_EmptyMap (0.00s)
    sheriff_test.go:510:
                Error Trace:    sheriff_test.go:510
                Error:          Not equal:
                                expected: "{\"a_map\":{}}"
                                actual  : "{\"a_map\":null}"

                                Diff:
                                --- Expected
                                +++ Actual
                                @@ -1 +1 @@
                                -{"a_map":{}}
                                +{"a_map":null}
                Test:           TestMarshal_EmptyMap
FAIL

[mweibel]

oh yeah, that looks like a bug. Wondering if that breaks existing users if we change it.. but would you be open to create a PR for it?

[mandeepji]

@mweibel created a PR. Can you review & let me know how can I trigger lint & test?