The customer was asking the meaning of this error:
Caused by: java.lang.IllegalArgumentException: Pool size must be set and > 0
These error details are shown in development mode. to switch it off, change the operatingMode in the jahia.properties config file.
operatingMode = production
The development environment was installed on a one core machine and this environment does not fit the minimal configuration as defined in our documentation :
https://academy.jahia.com/documentation/digital-experience-manager/7.2/technical/configuration-and-fine-tuning/prerequisites
Suggested Min. Development Configuration: