core/src/main/java/org/trimou/engine/MustacheEngineBuilder.java
public MustacheEngineBuilder registerHelpers(Map<String, Helper> helpers,
            boolean overwrite) {
        checkArgumentNotNull(helpers);
        checkNotBuilt();
        for (Entry<String, Helper> entry : helpers.entrySet()) {
            registerHelper(entry.getKey(), entry.getValue(), overwrite);
        }
        return this;
    }
public MustacheEngineBuilder registerHelpers(Map<String, Helper> helpers,
            boolean overwrite) {
        checkArgumentNotNull(helpers);
        checkNotBuilt();
        for (Entry<String, Helper> entry : helpers.entrySet()) {
            registerHelper(entry.getKey(), entry.getValue(), overwrite);
        }
        return this;
    }
Each helper must be registered with a unique name. If there is a helper
registered with the same name and the param <code>overwrite</code> is
<code>true</code> the previous instance is replaced, otherwise an
{@link IllegalArgumentException} is thrown.

@param helpers
@param overwrite
@return