A DESCRIPTION OF THE PROBLEM :
Since JDK 11.0.17 schema error "cvc-complex-type.4" is reported twice on schema validation when isSpecified == false and currDecl.fTargetNamespace == null (see src/java.xml/share/classes/com/sun/org/apache/xerces/internal/impl/xs/XMLSchemaValidator.java lines 3219++).
This behavior was introduced by commit https://github.com/openjdk/jdk11u-dev/commit/664f2abe79411e17bb7d2024fe2ba7fb9a7ab9ef to 11.0.17 GA (see https://github.com/openjdk/jdk11u-dev/commit/664f2abe79411e17bb7d2024fe2ba7fb9a7ab9ef#diff-559485fb84e5da2f5c0db2e967e6522895fb398da4d2eca9bd0f571461585b01).
When comparing this commit to the original change in the Xerces sources (see http://svn.apache.org/viewvc?view=revision&revision=1894472 or the according diff http://svn.apache.org/viewvc/xerces/java/trunk/src/org/apache/xerces/impl/xs/XMLSchemaValidator.java?r1=1871903&r2=1894472&pathrev=1908724) it looks like a merge conflict.
REGRESSION : Last worked in version 11
FREQUENCY : always