DecimalField invalid validation shows "required" error message

If I initialize a DecimalField with required set to true and input a letter then it shows: "This field is required." instead of saying something about the entry being invalid for example.

The issue identifies DecimalField but does not name a source file or test. Start by locating DecimalField's validation logic and the existing validation tests, then reproduce the case with required set to true and a letter as input. Done means invalid input produces an error describing the invalid value rather than the required-field message.

Written by the indexing model from the issue text.