is
  Indicates if it was possible for Gradle to determine which input files were out of date compared to a previous execution. Incremental inputs are unavailable when history is unavailable (i.e. this piece of work has never been executed before), or if there are changes to non-file input properties, or output files.
 When true: 
- getFileChanges and getFileChanges report changes to the input files compared to the previous execution.
 When false: 
- Every input file is reported via getFileChanges and getFileChanges as if it was ADDED.