The documentation for JQL searches states that only the CONTAINS operator ** is valid for the text field. Later in the documentation, it list ** and !~ as valid operators.

https://confluence.atlassian.com/jirasoftwareserver/advanced-searching-fields-reference-939938743.html#Advancedsearching-fieldsreference-textTextText

~! is not a valid operator for the text field in a JQL search.

Suggested change

The line which currently reads as follows:

The text master-field can only be used with the CONTAINS operator ("~" and "!~").

Should be modified to read as this:

The text master-field can only be used with the CONTAINS operator ("~").