Steps to reproduce:

• Use default camunda-bpm-ee-tomcat-7.10.0-ee
• Send the following GET request: localhost:8080/engine-rest/history/process-instance?startedAfter="makepizza"

Expected behaviour:

    "type": "InvalidRequestException",
    "message": "Cannot set query parameter 'startedAfter' to value ''makepizza'': Cannot convert value \"'makepizza'\" to java type java.util.Date"

Actual result:
The parameter is excluded / ignored from the filter and a 200 OK is returned if the rest of the query parameters are valid.

This has been tested with the startedAfter and startedBefore parameters of the following endpoint: https://docs.camunda.org/manual/7.10/reference/rest/history/process-instance/get-process-instance-query/ but it may affect other parameters / endpoints too.

Root cause

• The DateConverter we use in the REST API (https://github.com/camunda/camunda-bpm-platform/blob/master/engine-rest/engine-rest/src/main/java/org/camunda/bpm/engine/rest/dto/converter/DateConverter.java) always wraps the submitted value in double quotes and then gives it to Jackson.
• "makepizza" becomes ""makepizza"" and Jackson reads the first pair of double quotes as an empty string and returns null, which essentially means that the filter is not applied

Solution ideas

• Validate that the submitted value does not start or end with double quotes