• In string concatenations
• In the java.lang.StringBuilder#append() or java.lang.StringBuffer#append() methods
• In the methods of java.io.PrintWriter or java.io.PrintStream
• in the methods org.slf4j.Logger

In these cases, conversion to string will be handled by the underlying library methods, and the explicit call to toString() is not needed.

Example:

  System.out.println(this.toString())

After the quick-fix is applied:

  System.out.println(this)

Note that without the toString() call, the code semantics might be different: if the expression is null, then the null string will be used instead of throwing a NullPointerException.

Use the Report only when qualifier is known to be not-null option to avoid warnings for the values that could potentially be null.