fix: variables with "empty" default values should not be marked as re…

…quired

main.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"reflect"
 	"strings"
 	"text/template"
 
@@ -69,6 +70,9 @@ func showModuleMarkdown(module *tfconfig.Module) {
 				return ""
 			}
 		},
+		"isDefined": func(v interface{}) bool {
+			return reflect.ValueOf(v).Kind() != 0
+		},
 	})
 	template.Must(tmpl.Parse(markdownTemplate))
 	err := tmpl.Execute(os.Stdout, module)
@@ -99,7 +103,7 @@ Provider Requirements:
 
 ## Input Variables
 {{- range .Variables }}
-* {{ tt .Name }}{{ if .Default }} (default {{ json .Default | tt }}){{else}} (required){{end}}
+* {{ tt .Name }}{{ if isDefined .Default }} (default {{ json .Default | tt }}){{else}} (required){{end}}
 {{- if .Description}}: {{ .Description }}{{ end }}
 {{- end}}{{end}}