Create a new rule and name it appropriately.

Add a trigger

Select Issue transitioned event

Trigger the event from any workflow transition.

Condition

Boolean condition

Expression

Use the following expression:

%{trigger.issue.resolution} != null

Add an Action

Select Update field

Field

Select Remaining estimate (minutes)

Update to

Select Value returned by parser expression

Parser expression

Write the following expression with the expression editor in Numeric mode.

0

After importing the JSON file, make sure to check the configuration of the rule. Non-existing configuration elements (issue types, fields, values etc.) will be highlighted.

{
  "name" : "Remove remaining estimate when an issue is closed",
  "description" : "",
  "creator" : "admin",
  "status" : false,
  "triggerData" : "",
  "triggerType" : "ISSUE_TRANSITIONED_EVENT",
  "configuration" : {
    "refs" : [ "issue", "system", "trigger.issue", "trigger.parent" ],
    "triggerType" : ""
  },
  "children" : [ {
    "sequence" : 0,
    "type" : "BOOLEAN_CONDITION",
    "ruleEntityType" : "CONDITION",
    "configuration" : {
      "refs" : [ "issue", "project", "system", "trigger", "trigger.issue", "trigger.parent" ],
      "expression" : "%{trigger.issue.resolution} != null",
      "expressionParsingMode" : "logical",
      "actingUser" : "field_00020"
    },
    "children" : [ {
      "sequence" : 0,
      "type" : "UPDATE_FIELD",
      "ruleEntityType" : "ACTION",
      "configuration" : {
        "refs" : [ "issue", "project", "system", "trigger", "trigger.issue", "trigger.parent" ],
        "fieldId" : "00024",
        "mode" : "parser",
        "value" : "0",
        "valueParsingMode" : "math",
        "actingUser" : "field_00020"
      },
      "children" : null,
      "hasChildren" : false
    } ],
    "hasChildren" : true
  } ],
  "hasChildren" : true
}