NPE in ModelUtils.isFreeFormObject

[padamstx]

Description

The attached apispec causes an NPE in ModelUtils.isFreeFormObject(). Within the apispec, the "Context" schema is defined like this:

            "Context":{
                "type":"object",
                "description":"A collection of arbitrary properties that form the context information for a message.",
                "additionalProperties":{
                    "type":"object"
                }
            }

The fact that additionalProperties is set to an ObjectSchema that contains no properties seems to be the crux of the problem. Which is odd because that's a fairly common construct.

openapi-generator version

master (latest)

OpenAPI declaration file content or url

I'm attaching the full apispec which can serve as a testcase:
testcase.zip

Steps to reproduce

Process the attached apispec with the "java" generator, with a command similar to this:

java -jar <location-of-jar>/openapi-generator-cli.jar generate -i testcase.json -g java -o ./java

Here is an example:

$ java -jar /work/openapitools/openapi-generator/modules/openapi-generator-cli/target/openapi-generator-cli.jar generate -i testcase.json -g java -o ./java/testcase
[main] WARN  o.o.c.ignore.CodegenIgnoreProcessor - Output directory does not exist, or is inaccessible. No file (.openapi-generator-ignore) will be evaluated.
[main] INFO  o.o.c.languages.AbstractJavaCodegen - Environment variable JAVA_POST_PROCESS_FILE not defined so the Java code may not be properly formatted. To define it, try 'export JAVA_POST_PROCESS_FILE="/usr/local/bin/clang-format -i"' (Linux/Mac)
[main] INFO  o.o.c.languages.AbstractJavaCodegen - NOTE: To enable file post-processing, 'enablePostProcessFile' must be set to `true` (--enable-post-process-file for CLI).
[main] WARN  o.o.codegen.utils.URLPathUtils - 'host' (OAS 2.0) or 'servers' (OAS 3.0) not defined in the spec. Default to [http://localhost] for server URL [http://localhost/]
[main] WARN  o.o.codegen.utils.URLPathUtils - 'host' (OAS 2.0) or 'servers' (OAS 3.0) not defined in the spec. Default to [http://localhost] for server URL [http://localhost/]
Exception in thread "main" java.lang.RuntimeException: Could not process model 'Message'.Please make sure that your schema is correct!
	at org.openapitools.codegen.DefaultGenerator.generateModels(DefaultGenerator.java:457)
	at org.openapitools.codegen.DefaultGenerator.generate(DefaultGenerator.java:888)
	at org.openapitools.codegen.cmd.Generate.run(Generate.java:355)
	at org.openapitools.codegen.OpenAPIGenerator.main(OpenAPIGenerator.java:62)
Caused by: java.lang.NullPointerException
	at org.openapitools.codegen.utils.ModelUtils.isFreeFormObject(ModelUtils.java:560)
	at org.openapitools.codegen.utils.ModelUtils.unaliasSchema(ModelUtils.java:772)
	at org.openapitools.codegen.DefaultCodegen.unaliasPropertySchema(DefaultCodegen.java:3403)
	at org.openapitools.codegen.DefaultCodegen.fromModel(DefaultCodegen.java:1708)
	at org.openapitools.codegen.languages.AbstractJavaCodegen.fromModel(AbstractJavaCodegen.java:942)
	at org.openapitools.codegen.DefaultGenerator.processModels(DefaultGenerator.java:1126)
	at org.openapitools.codegen.DefaultGenerator.generateModels(DefaultGenerator.java:452)
	... 3 more

Related issues/PRs

Suggest a fix/enhancement

I'll submit a PR that fixes the issue.

[padamstx]

It seems that I'm unable to assign this issue to myself as I'm a new contributor to the project, but I've submitted a PR with the fix.