[BUG][JAVA] openapi-generator version >= 6.2 doesn't generate examples for allOf attributes

Description

Generate the open api json using openapi-generator-cli-6.2.0.jar or above and it doesn't generate examples for allOf attribute.
When viewed with swagger viewer, the example shows 'null', whereas the expectation is a json generated by combining all the schema's of allOf with values as datatypes. Its working fine in openapi-generator-cli-6.1.0.jar

Behavior in 6.2 and above

Expected behavior

openapi-generator version

Seen in openapi-generator-cli-6.2.0.jar - openapi-generator-cli-6.3.0.jar

Steps to reproduce

compile the spec yaml using openapi-generator-cli-6.2.0.jar or above and it will generate the json with example null

java -jar openapi-generator-cli-6.2.0.jar generate -i api-spec/openapi.yaml  -g openapi  -o api-spec/static --additional-properties outputFileName=openapi.json;

Start with api-spec/openapi.yaml and reproduce the issue using the documented Java command with openapi-generator-cli 6.1.0, 6.2.0, and 6.3.0. Compare the generated api-spec/static/openapi.json output for an allOf schema. Done means the generated example combines the allOf schemas with datatype values instead of null, with coverage for the regression.