code: protected KieBase getKnowledgeBase(String name, String assetVersion, String modifier) throws ActivityException {
          Map<String,String> customAttrs = null;
          KnowledgeBaseAsset kbrs;
          if (assetVersion == null)
              kbrs = DroolsKnowledgeBaseCache.getKnowledgeBaseAsset(name, modifier, customAttrs, getClassLoader());
          else
              kbrs = DroolsKnowledgeBaseCache.getKnowledgeBaseAsset(new AssetVersionSpec(name, assetVersion), modifier, customAttrs, getClassLoader());
  
          if (kbrs == null) {
              return null;
          }
          else {
              super.loginfo("Using Knowledge Base: " + kbrs.getAsset().getLabel());
  
              String versionLabelVarName = getAttributeValue(RULE_VERSION_VAR);
              if (versionLabelVarName != null)
                  setParameterValue(versionLabelVarName, kbrs.getAsset().getLabel());
              return kbrs.getKnowledgeBase();
          }
      }
docs: Returns the asset based on specified version/range whose attributes match the custom attribute
  Override to apply additional or non-standard conditions.