Fixes #722

This commit: 3ac195e#diff-371437d4e9e09ea18f2ff29dbacd0e84R4315 seems to forgotten to add formParams for `addCodegenContentParameters` function

Author: UnHumbleBen

src/main/java/io/swagger/codegen/v3/generators/DefaultCodegenConfig.java

@@ -4313,6 +4313,7 @@ protected void addParameters(CodegenContent codegenContent, List<CodegenParamete
     protected void addCodegenContentParameters(CodegenOperation codegenOperation, List<CodegenContent> codegenContents) {
         for (CodegenContent content : codegenContents) {
             addParameters(content, codegenOperation.bodyParams);
+            addParameters(content, codegenOperation.formParams);
             addParameters(content, codegenOperation.headerParams);
             addParameters(content, codegenOperation.queryParams);
             addParameters(content, codegenOperation.pathParams);