ENH: Server parses `nan` to Double in all upper/lowercase variations

src/main/java/caosdb/server/datatype/DoubleDatatype.java

@@ -20,6 +20,7 @@
  *
  * ** end header
  */
+// Copyright (c) 2019 Daniel Hornung
 package caosdb.server.datatype;
 
 import caosdb.server.entity.Message;
@@ -34,7 +35,11 @@ public class DoubleDatatype extends AbstractDatatype {
       if (value instanceof GenericValue) {
         return new GenericValue(Double.parseDouble(((GenericValue) value).toDatabaseString()));
       } else {
-        return new GenericValue(Double.parseDouble(value.toString()));
+        String valueStr = value.toString();
+        if (valueStr.toLowerCase().equals("nan")) {
+          valueStr = "NaN";
+        }
+        return new GenericValue(Double.parseDouble(valueStr));
       }
     } catch (final NumberFormatException e) {
       throw ServerMessages.CANNOT_PARSE_DOUBLE_VALUE;