Fixes #1: SchemaExtension constructor throws NPE

Author: Robert Winkler

build.gradle

@@ -12,7 +12,7 @@ buildscript {
 
 subprojects {
     description = 'Swagger2Markup extensions.'
-    version = '1.0.0'
+    version = '1.0.1-SNAPSHOT'
     group = 'io.github.swagger2markup'
 
     apply plugin: 'java'

swagger2markup-import-schemas-ext/src/main/java/io/github/swagger2markup/extensions/SchemaExtension.java

@@ -73,7 +73,6 @@ public SchemaExtension(URI schemaBaseUri) {
      */
     public SchemaExtension(String extensionId, URI schemaBaseUri) {
         super();
-        Validate.notNull(extensionId);
         Validate.notNull(schemaBaseUri);
         if(StringUtils.isNoneBlank(extensionId)) {
             this.extensionId = extensionId;