Refine exception message

Closes gh-4569

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/condition/SpringBootCondition.java

@@ -51,10 +51,11 @@ public abstract class SpringBootCondition implements Condition {
 		}
 		catch (NoClassDefFoundError ex) {
 			throw new IllegalStateException("Could not evaluate condition on "
-					+ classOrMethodName + " due to internal class not found. "
-					+ "This can happen if you are @ComponentScanning a "
-					+ "springframework package (e.g. if you put a @ComponentScan "
-					+ "in the default package by mistake)", ex);
+					+ classOrMethodName + " due to " + ex.getMessage() + " not "
+					+ "found. Make sure your own configuration does not rely on "
+					+ "that class. This can also happen if you are "
+					+ "@ComponentScanning a springframework package (e.g. if you "
+					+ "put a @ComponentScan in the default package by mistake)", ex);
 		}
 		catch (RuntimeException ex) {
 			throw new IllegalStateException(