core/src/main/java/org/springframework/security/core/authority/mapping/MapBasedAttributes2GrantedAuthoritiesMapper.java
private Map<String, Collection<GrantedAuthority>> preProcessMap(Map<?, ?> orgMap) {
		Map<String, Collection<GrantedAuthority>> result = new HashMap<String, Collection<GrantedAuthority>>(
				orgMap.size());

		for (Map.Entry<?, ?> entry : orgMap.entrySet()) {
			Assert.isInstanceOf(String.class, entry.getKey(),
					"attributes2grantedAuthoritiesMap contains non-String objects as keys");
			result.put((String) entry.getKey(),
					getGrantedAuthorityCollection(entry.getValue()));
		}
		return result;
	}
private Map<String, Collection<GrantedAuthority>> preProcessMap(Map<?, ?> orgMap) {
		Map<String, Collection<GrantedAuthority>> result = new HashMap<String, Collection<GrantedAuthority>>(
				orgMap.size());

		for (Map.Entry<?, ?> entry : orgMap.entrySet()) {
			Assert.isInstanceOf(String.class, entry.getKey(),
					"attributes2grantedAuthoritiesMap contains non-String objects as keys");
			result.put((String) entry.getKey(),
					getGrantedAuthorityCollection(entry.getValue()));
		}
		return result;
	}
Preprocess the given map to convert all the values to GrantedAuthority collections

@param orgMap The map to process
@return the processed Map