better failure diagnostic and logging

jps/jps-builders/src/org/jetbrains/jps/incremental/IncProjectBuilder.java

@@ -186,6 +186,7 @@ public class IncProjectBuilder {
       if (cause instanceof PersistentEnumerator.CorruptedException ||
           cause instanceof MappingFailedException ||
           cause instanceof IOException) {
+        LOG.info(e);
         myMessageDispatcher.processMessage(new CompilerMessage(
           "", BuildMessage.Kind.INFO,
           "Internal caches are corrupted or have outdated format, forcing project rebuild: " +
@@ -204,6 +205,7 @@ public class IncProjectBuilder {
           }
         }
         else {
+          LOG.info(e);
           // the reason for the build stop is unexpected internal error, report it
           myMessageDispatcher.processMessage(new CompilerMessage("", cause));
         }

jps/jps-builders/src/org/jetbrains/jps/incremental/messages/CompilerMessage.java

@@ -15,6 +15,7 @@
  */
 package org.jetbrains.jps.incremental.messages;
 
+import com.intellij.openapi.util.text.StringUtil;
 import org.jetbrains.annotations.Nullable;
 
 import java.io.ByteArrayOutputStream;
@@ -101,7 +102,7 @@ public class CompilerMessage extends BuildMessage {
     StringBuilder text = new StringBuilder();
     text.append("Error: ");
     final String msg = internalError.getMessage();
-    if (msg != null) {
+    if (!StringUtil.isEmptyOrSpaces(msg)) {
       text.append(msg);
     }
     else {