diff --git a/build.gradle b/build.gradle
index 98c6903c..eb0dacb8 100644
--- a/build.gradle
+++ b/build.gradle
@@ -17,9 +17,9 @@ plugins {
     id "io.freefair.lombok" version "6.1.0"
     id "io.freefair.maven-publish-java" version "6.1.0"
     id "io.spring.dependency-management" version "1.0.7.RELEASE" 
-    id "com.github.kt3k.coveralls" version "2.8.1" 
+    //id "com.github.kt3k.coveralls" version "2.8.1" 
     id "org.owasp.dependencycheck" version "3.1.2"
-    id "org.ajoberstar.grgit" version "2.0.1"
+    //id "org.ajoberstar.grgit" version "2.0.1"
     id "com.jfrog.bintray" version "1.7.3"
     id "java"
     id "jacoco"
diff --git a/src/main/java/edu/kit/datamanager/util/json/CustomInstantDeserializer.java b/src/main/java/edu/kit/datamanager/util/json/CustomInstantDeserializer.java
index ccbbfdad..ebcc44e8 100644
--- a/src/main/java/edu/kit/datamanager/util/json/CustomInstantDeserializer.java
+++ b/src/main/java/edu/kit/datamanager/util/json/CustomInstantDeserializer.java
@@ -29,6 +29,8 @@
 import java.time.format.DateTimeParseException;
 import java.time.temporal.ChronoField;
 import java.time.temporal.ChronoUnit;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  *
@@ -36,6 +38,8 @@
  */
 public class CustomInstantDeserializer extends JsonDeserializer<Instant> {
 
+    private static final Logger LOGGER = LoggerFactory.getLogger(CustomInstantDeserializer.class);
+
     private final DateTimeFormatter isoFormat = DateTimeFormatter.ISO_DATE_TIME.withZone(ZoneOffset.UTC);
     //additional date patterns according to DataCite JSON spec ordered by probability of use
     private final DateTimeFormatter[] additionalFormats = new DateTimeFormatter[]{
@@ -53,23 +57,26 @@ public class CustomInstantDeserializer extends JsonDeserializer<Instant> {
 
     @Override
     public Instant deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
-        if (p.getText() == null || p.getText().length() == 0) {
+        String text = p.getText();
+        if (text == null || text.length() == 0) {
             return null;
         }
 
         try {
-            return Instant.from(isoFormat.parse(p.getText())).truncatedTo(ChronoUnit.MILLIS);
+            LOGGER.trace("Trying to parse date {} using ISO_DATE_TIME.", text);
+            return Instant.from(isoFormat.parse(text)).truncatedTo(ChronoUnit.MILLIS);
         } catch (DateTimeParseException ex) {
             //no iso format...continue with other formats
+            LOGGER.trace("Date {} is no ISO_DATE_TIME, trying alternatives.", text);
         }
         for (DateTimeFormatter formatter : additionalFormats) {
             try {
-                LocalDate date = LocalDate.from(formatter.parse(p.getText()));
+                LOGGER.trace("Parsing date {} using formatter {}.", text, formatter);
+                LocalDate date = LocalDate.from(formatter.parse(text));
                 return Instant.from(date.atStartOfDay(ZoneOffset.UTC).toInstant());
-            } catch (DateTimeParseException ex) {
-                //no valid date according to the current format, continue if possible
             } catch (DateTimeException ex) {
-                ex.printStackTrace();
+                //no valid date according to the current format, continue if possible
+                LOGGER.trace("Date {} cannot be parsed using formatter {}.", text, formatter);
             }
         }
         throw new DateTimeParseException("Invalid date string. Supported format patterns are: yyyy-MM-dd'T'HH:mm:ss'Z', yyyy, yyyy-MM-dd and yyyy-MM", p.getText(), 0);