Multiple Nullpointer warnings while upgrading in DDMFieldUpgradeProcess

Issue

• Many warnings appears while upgrading Liferay DXP 7.4 from previous versions, affecting the DDMFieldUpgradeProcess (v4_1_0):
  

  INFO  [main][UpgradeProcess:118] Upgrading com.liferay.dynamic.data.mapping.internal.upgrade.v4_1_0.DDMFieldUpgradeProcess
  WARN  [main][DDMFieldUpgradeProcess:533] null
  java.lang.NullPointerException: null
      at com.liferay.dynamic.data.mapping.storage.DDMFormFieldValue.getType(DDMFormFieldValue.java:131) ~[?:?]
      at com.liferay.dynamic.data.mapping.internal.upgrade.v4_1_0.DDMFieldUpgradeProcess._upgradeDDMFormValuesHierarchy(DDMFieldUpgradeProcess.java:529) ~[?:?]
      at com.liferay.dynamic.data.mapping.internal.upgrade.v4_1_0.DDMFieldUpgradeProcess._upgradeDDMContent(DDMFieldUpgradeProcess.java:405) ~[?:?]
      at com.liferay.dynamic.data.mapping.internal.upgrade.v4_1_0.DDMFieldUpgradeProcess.doUpgrade(DDMFieldUpgradeProcess.java:133) ~[?:?]

Environment

• Migrating to DXP 7.4 U40+ or Quarterly Releases.

Resolution

• Upgrade process should finish with a warning status with Liferay DXP 7.4 U41+ or higher.
• Create a support ticket requesting a hotfix for LPD-21792, LPD-22327 and LPS-198028 if not fixed in the target Quarterly Release.
• Under certain circumstances, this message could be ignored once reviewed by the Liferay support team.

Additional Information

• LPS-160305 - Removing field from Form causes null exception when upgrading
• LPS-198028 - Unable to migrate DDMContent to DDMField and DDMFieldAttribute
• LPD-21792 - Unable to find dynamic data mapping structure when upgrading from 7.0
• LPD-22327 - Parent DDMStructure values are not showing when editing the Child DDL record