Answers.Body: <p>I'll dig deeper in another post, but as far as this problem was concerned, I used print and var_dump to trace the problem to </p>
  
  <pre><code>public static function getReferencesToTable
  .
  .
  .
  $links = $daoClassName::getReferenceColumns();
  </code></pre>
  
  <p>'crashes' because one of the classes was NULL. </p>
  
  <p>While I work on WHY, I got around the crash with a simple:</p>
  
  <pre><code>if ( $daoClassName != NULL)
  </code></pre>
  
  <p>wrapper.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-02-03T01:29:11.820Z
Answers.LastActivityDate: 2020-02-03T01:29:11.820Z
Answers.UserDisplayName: Mike Steigerwald
Body: <p>Using civicrm-5.21.2-wordpress.zip, (and also 5.20), I get a 'crash' ('There has been a critical error on your website. Please check your site admin email inbox for instructions.') for any attempt to merge contacts.</p>
  
  <p>None of the WordPress trouble-shooting info has helped. I don't get any CiviCRM trace-back or debugging data. I don't see anything in the Apache error.log .</p>
  
  <p>Any other suggestions for trouble-shooting this?</p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-01-26T00:22:07.447Z
Comments.Text: does the civi log have any further details?
Comments.UserDisplayName: ericG
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-01-26T00:29:27.777Z
Comments.Text: what version of php are you running?
Comments.UserDisplayName: ericG
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-01-26T00:31:15.367Z
Comments.Text: you can use this extension for easier access to the civicrm logs where there might be some more info
  https://civicrm.org/extensions/civicrm-log-viewer
Comments.UserDisplayName: ericG
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-01-26T00:33:27.803Z
Comments.Text: I'm on php 7.2.24. I'm not familiar with civi log, so I'll eagerly install that extension!
Comments.UserDisplayName: Mike Steigerwald
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-01-26T00:43:37.927Z
Comments.Text: The civi logs don't have any errors for the past several days.
Comments.UserDisplayName: Mike Steigerwald
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-01-26T00:50:20.147Z
Comments.Text: I don't use wordpress often, that's a wordpress generated error message but I don't know how that relates to civi errors. sorry
Comments.UserDisplayName: ericG
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-01-28T11:09:04.360Z
Comments.Text: You should get a mail to your site admin address with more detail - what does it say?
Comments.UserDisplayName: Aidan
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-01-29T14:31:27.443Z
Comments.Text: I never got that email. I'm working on 'why' as a separate issue.
Comments.UserDisplayName: Mike Steigerwald
Tags: <duplicate-contacts>
Title: How to trouble-shoot 'critical error' while merging duplicates?
ThreadText: # How to trouble-shoot 'critical error' while merging duplicates?
  
  (Asked by: username_0 on 2020-01-25)
  
  Using civicrm-5.21.2-wordpress.zip, (and also 5.20), I get a 'crash' ('There has been a critical error on your website. Please check your site admin email inbox for instructions.') for any attempt to merge contacts.
  
  None of the WordPress trouble-shooting info has helped. I don't get any CiviCRM trace-back or debugging data. I don't see anything in the Apache error.log .
  
  Any other suggestions for trouble-shooting this?
  
  **Tags:** duplicate-contacts
  
  > **Comments:**
  > **username_1**: does the civi log have any further details?  
  > **username_1**: what version of php are you running?  
  > **username_1**: you can use this extension for easier access to the civicrm logs where there might be some more info https://civicrm.org/extensions/civicrm-log-viewer  
  > **username_0**: I'm on php 7.2.24. I'm not familiar with civi log, so I'll eagerly install that extension!  
  > **username_0**: The civi logs don't have any errors for the past several days.  
  > **username_1**: I don't use wordpress often, that's a wordpress generated error message but I don't know how that relates to civi errors. sorry  
  > **username_2**: You should get a mail to your site admin address with more detail - what does it say?  
  > **username_0**: I never got that email. I'm working on 'why' as a separate issue.  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_0 on 2020-02-03. Score: 0 | Accepted answer
  
  I'll dig deeper in another post, but as far as this problem was concerned, I used print and var_dump to trace the problem to 
  public static function getReferencesToTable
  .
  .
  .
  $links = $daoClassName::getReferenceColumns();
  
  'crashes' because one of the classes was NULL. 
  While I work on WHY, I got around the crash with a simple:
  if ( $daoClassName != NULL)
  
  wrapper.
  
  
  ---
  
  