PAN-50 Addressed Brittany's comment about logging consistency

persistence/src/main/java/edu/msudenver/tsp/persistence/controller/DefinitionController.java

@@ -85,7 +85,7 @@ public class DefinitionController {
         }
 
         if (definitionDto == null) {
-            LOG.error("Passed entity is unprocessable");
+            LOG.error("Passed entity is null");
             return new ResponseEntity<>(HttpStatus.BAD_REQUEST);
         }
 

persistence/src/main/java/edu/msudenver/tsp/persistence/controller/TheoremController.java

@@ -130,7 +130,7 @@ public class TheoremController {
         }
 
         if (theoremDto == null) {
-            LOG.error("Passed entity is unprocessable");
+            LOG.error("Passed entity is null");
             return new ResponseEntity<>(HttpStatus.BAD_REQUEST);
         }