added null check per #16

Author: fehguy

modules/swagger-compat-spec-parser/src/main/java/io/swagger/parser/SwaggerCompatConverter.java

@@ -180,7 +180,8 @@ else if(ParamType.FORM.equals(param.getParamType())) {
 
     output.setName(param.getName());
     output.setDescription(param.getDescription());
-    output.setRequired(param.getRequired());
+    if(param.getRequired() != null)
+      output.setRequired(param.getRequired());
 
     Property property = null;
     String type = param.getType() == null ? null : param.getType().toString();