[BUG] Java Maven Openapi generator returns a Null Pointer Exception.

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

I did the validation in the YAML file and it passes, however, when I try to generate the code from this YAML file API it returns the error below:

  Exception: null
    at org.openapitools.codegen.DefaultGenerator.processOperation (DefaultGenerator.java:1204)
    at org.openapitools.codegen.DefaultGenerator.processPaths (DefaultGenerator.java:1098)
    at org.openapitools.codegen.DefaultGenerator.generateApis (DefaultGenerator.java:556)
    at org.openapitools.codegen.DefaultGenerator.generate (DefaultGenerator.java:1008)
    at org.openapitools.codegen.plugin.CodeGenMojo.execute (CodeGenMojo.java:746)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:957)
    at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:289)
    at org.apache.maven.cli.MavenCli.main (MavenCli.java:193)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62)
    at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke (Method.java:566)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
Caused by: java.lang.NullPointerException
    at org.openapitools.codegen.DefaultCodegen.fromRequestBodyToFormParameters (DefaultCodegen.java:5458)
    at org.openapitools.codegen.DefaultCodegen.fromOperation (DefaultCodegen.java:3506)
    at org.openapitools.codegen.languages.AbstractJavaCodegen.fromOperation (AbstractJavaCodegen.java:1226)
    at org.openapitools.codegen.DefaultGenerator.processOperation (DefaultGenerator.java:1172)
    at org.openapitools.codegen.DefaultGenerator.processPaths (DefaultGenerator.java:1098)
    at org.openapitools.codegen.DefaultGenerator.generateApis (DefaultGenerator.java:556)
    at org.openapitools.codegen.DefaultGenerator.generate (DefaultGenerator.java:1008)
    at org.openapitools.codegen.plugin.CodeGenMojo.execute (CodeGenMojo.java:746)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:957)
    at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:289)
    at org.apache.maven.cli.MavenCli.main (MavenCli.java:193)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62)
    at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke (Method.java:566)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)

openapi-generator version

• 4.3.1

OpenAPI declaration file content or url

The URL code: https://github.com/platformsh/platformsh-client-java/blob/master/src/main/resources/api.yaml

Command line used for generation

On this project source code: https://github.com/platformsh/platformsh-client-java
We run this command:

mvn clean package

Steps to reproduce

git clone git@github.com:platformsh/platformsh-client-java.git
cd platformsh-client-java
mvn clean package

Related issues/PRs

Suggest a fix

Clone platformsh-client-java and run mvn clean package to reproduce the failure. Start at DefaultCodegen.fromRequestBodyToFormParameters and trace the call through DefaultGenerator.processOperation and AbstractJavaCodegen.fromOperation using the referenced api.yaml. Done means the valid specification generates successfully without a NullPointerException.