Don't call getValue when getting namespace

Fixes #177

Signed-off-by: Gary O'Neall <gary@sourceauditor.com>

Author: goneall

src/main/java/org/spdx/library/model/ExternalDocumentRef.java

@@ -183,7 +183,7 @@ public ExternalDocumentRef setChecksum(Checksum checksum) throws InvalidSPDXAnal
 	 * @return the spdxDocumentNamespace or empty string if no namespace
 	 */
 	public String getSpdxDocumentNamespace() throws InvalidSPDXAnalysisException {
-		Optional<Object> docNamespace = getObjectPropertyValue(SpdxConstants.PROP_EXTERNAL_SPDX_DOCUMENT);
+		Optional<Object> docNamespace = getModelStore().getValue(getDocumentUri(), getId(), SpdxConstants.PROP_EXTERNAL_SPDX_DOCUMENT);
 		if (!docNamespace.isPresent()) {
 			logger.warn("SPDX document namespace not found");
 			return "";

src/main/java/org/spdx/library/model/ExternalSpdxElement.java

@@ -196,8 +196,8 @@ public static ExternalSpdxElement uriToExternalSpdxElement(String uri,
 
 	public static String externalDocumentIdToNamespace(String externalDocumentId,
 			IModelStore stModelStore, String stDocumentUri, ModelCopyManager copyManager) throws InvalidSPDXAnalysisException {
-		Optional<Object> retval = getObjectPropertyValue(stModelStore, stDocumentUri, 
-				externalDocumentId, SpdxConstants.PROP_EXTERNAL_SPDX_DOCUMENT, copyManager);
+
+		Optional<Object> retval = stModelStore.getValue(stDocumentUri, externalDocumentId, SpdxConstants.PROP_EXTERNAL_SPDX_DOCUMENT);
 		if (!retval.isPresent()) {
 			throw new InvalidSPDXAnalysisException("No external document reference exists for document ID "+externalDocumentId);
 		}