Improve error message for reader and visitor

Closes gh-292

(cherry picked from commit d5b9778)

Author: ttddyy

micrometer-docs-generator/src/main/java/io/micrometer/docs/commons/AbstractSearchingFileVisitor.java

@@ -103,7 +103,7 @@ protected void validateNameOrConvention(String name, @Nullable String convention
         if (StringUtils.hasText(name)) {
             if (conventionClassName != null) {
                 throw new IllegalStateException(
-                        "You can't declare both [getName()] and [getDefaultConvention()] methods at the same time, you have to chose only one. Problem occurred in ["
+                        "You can't declare both [getName(),getContextualName()] and [getDefaultConvention()] methods at the same time, you have to chose only one. Problem occurred in ["
                                 + enclosingEnum.getName() + "] class");
             }
         }

micrometer-docs-generator/src/main/java/io/micrometer/docs/commons/EventEntryForSpanEnumConstantReader.java

@@ -39,7 +39,9 @@ public Class<?> getRequiredClass() {
     public EventEntry apply(EnumConstantSource enumConstantSource) {
         String description = AsciidocUtils.javadocToAsciidoc(enumConstantSource.getJavaDoc());
         String name = ParsingUtils.enumMethodValue(enumConstantSource, "getContextualName");
-        Assert.notNull(name, "Event enum constants require readable getContextualName() for spans documentation.");
+        Assert.notNull(name,
+                String.format("Event enum constants require readable getContextualName() for spans documentation. [%s]",
+                        enumConstantSource.getName()));
 
         EventEntry model = new EventEntry();
         model.setName(name);